Urban agriculture in Honolulu

UH News

Hawaiʻi’s heavy reliance on imported goods and the future impact of climate change on food production are just two of the reasons why a UH Mānoa global environmental science senior focused her project on urban agriculture (vertical farming, community gardens, hydroponics and greenhouses) in Honolulu. In this public impact research project, Seraphina King conducted interviews with stakeholders, and reviewed existing literature and case studies to determine how Honolulu government and non-governmental organizations are engaging in urban agriculture.

“The research is ongoing. So far, I would say that urban agriculture could have positive outcomes for Honolulu,” King said. “However, it is hard to implement due to competing land uses and current policies that limit zoning. My research seems to point to what some scholars have said about urban agriculture—it cannot be a substitute for food imports but could bolster community resilience.”

King, who was mentored by Department of Urban and Regional Planning Associate Professor Priyam Das, said she hoped attendees of her presentation gained a “better understanding of urban agriculture and what it can offer in terms of expanding food production in cities.” She added, “It might even spark interest in thinking of ways they want to become engaged in urban agriculture projects in their communities.”

University of Hawaii breaks ground on food entrepreneurship facility

Pacific Business News
By Janis L. Magin

The University of Hawaii Community Colleges broke ground this week and plans to start construction in July on the Wahiawa Product Development Center in Central Oahu.

The $12 million project will turn a metal warehouse at 100 California Ave. into a value-added product development center where students from Leeward Community College can learn entrepreneurship skills while developing value-added food products.

Students will be able to develop products such as baked goods, pickled products, ice creams and juices, which will help local farmers utilize off-grade produce as ingredients, minimizing food waste.

“The Wahiawa Product Development Center will be instrumental in supporting the diversification of our local economy by adding value to Hawaii’s agricultural and food sector industries,” UH Community Colleges Vice President Erika Lacro said in a statement. “It will take the knowledge, creativity, innovation and uniqueness Hawaii offers to the next level, creating a robust workforce pipeline and providing the tools and skills for local farmers and entrepreneurs to take their value-added food products to market and beyond. Bringing this to the heart of Oahu achieves a critical milestone for our state in food security and sustainability.”

The state Department of Agriculture’s Agribusiness Development Corp. bought the property from Tamura’s in November 2013 for $4.29 million, and UH launched plans for the center in late 2019 with the publication of a draft environmental assessment. Ushijima Architects is designing the project.

“Products that are made-in-Hawaii are highly desired worldwide and we have a huge opportunity with the WPDC to capitalize on that global demand. Value-added entrepreneurship is critical for economic recovery as we look to strengthen the agricultural industry and diversify our economy to be less reliant on tourism,” state Sen. Donovan Dela Cruz said in a statement. “Wahiawa welcomes this community investment and looks forward to working with the University of Hawaii in the years to come.”

Don’t waive the Jones Act — scrap it, by Bloomberg News

Keene Sentinel

Another domestic energy crisis, another waiver of the Jones Act. –

In response to the ransomware attack on the Colonial Pipeline, which delivers about 45 percent of the fuel for the Eastern Seaboard, President Joe Biden’s administration said that it would allow two exemptions to the 101-year-old act, which restricts waterborne commerce between U.S. ports to ships that are built, crewed and owned by Americans. Citgo Petroleum Corp. and Valero Energy Corp. now have permission to use foreign vessels to transport oil products between the Gulf Coast and the East Coast

Hurricanes forced previous presidents to suspend the law to ensure deliveries of food, fuel and other goods. This time, Biden should face reality and bury it under the waves.

As with most protectionist measures, the Jones Act harms the very people it purports to help. Because oceangoing Jones Act-compliant ships are more expensive, and there aren’t that many of them, the law leads to higher prices for goods, more congested roadways and pipelines, and additional pollution from greater reliance on carbon-intensive transportation.

Its market-bending distortions could scarcely be exaggerated. As a direct result of the law, refineries on both coasts can find it cheaper to import foreign oil than to use domestic sources. Refineries in the Gulf Coast choose to send their products to Latin America instead of the East Coast. The U.S. may be a natural gas powerhouse, but it has no Jones Act-compliant liquefied natural gas carriers, which would cost two to three times as much as equivalent ships from South Korea. So Puerto Rico and Hawaii source their LNG from overseas, northeast ports look to Trinidad and Tobago, and U.S. natural gas goes abroad.

The act is even undermining the Biden administration’s vaunted green-energy plans. Offshore wind projects need Jones Act-compliant turbine-installation vessels. Right now, the U.S. has one — under construction, that is, and due to launch in 2023 at a cost of $500 million. Hitting the administration’s goal of 30 gigawatts of offshore wind-energy production by 2030 will require more vessels, which the law will only make more expensive.

It would be one thing if the Jones Act met its stated goal of sustaining a robust merchant fleet. But the number of Jones Act-eligible U.S. vessels in 2019 was 99, versus 193 in 2000. From 1960 to 2014, even as U.S. output more than quadrupled, the tonnage of domestic contiguous coastal shipping dropped by 44 percent. America’s few remaining commercial shipyards are expensive and superannuated: Indeed, some companies that shamelessly defend their Jones Act monopolies send their ships to China for repairs, which is cheaper even with the 50 percent tariff that they pay the U.S. government for the privilege.

The Jones Act survives because it supports the narrow interests of a handful of shipping companies and maritime unions, which pump out a reliable stream of campaign cash to the Congressional Shipbuilding Caucus. Never mind the costs to all Americans — especially those in Alaska, Hawaii and Puerto Rico, who depend heavily on maritime commerce.

There are better ways to build up coastal commerce and the maritime industry, from investing in neglected port infrastructure and public shipyards to changing the tax treatment of U.S.-flagged ships. Yet the Biden administration seems committed to preserving the Jones Act, whatever the consequences. Here’s a question for the White House to ponder: If this law is so successful and so vital, why does it so often need to be waived in cases of emergency?

PARC working on agricultural promotion to ensure food security in Thar

Associated Press of Pakistan

ISLAMABAD, Dec 29 (APP): Pakistan Agriculture Research Council (PARC) was working to ensure food security in Thar desert and for the purpose it had cultivated different kinds of fruits, vegetables and fodder crops to promote agriculture sector and create livelihood opportunities for the locals.

Talking to APP on Tuesday the Chairman PARC Dr Muhammad Azeem said the Council was engaged to strengthen government’s efforts to eliminate malnutrition and hunger by intervening through agriculture and livestock development.

The PARC, he said, in collaboration with non-governmental organisations had developed different farmers cluster and was providing seeds of different beans to to the farmers to enhance yields.

“We are providing about 200 to 300 mounds seeds of different beans, besides providing 50 to 60 mound bean for the farmers of Tharparker, he added.

“We are also working on preservation of local species and preserved about 50 local species including trees, medicinal plants and cultivated moringa”.

Meanwhile, Dr Attaullah Director PARC North Zone told that 14 varieties of guava, matching the local ecology, were also developed and distributed among the farmers to develop fruit orchids.

Besides, 38 varieties of dates were also grown and 13 types of different grasses over 10 acres of land were also grown, he said adding that these interventions had helped create livelihood opportunities as well as fulfilling the food requirements of the local communities.

Meanwhile, forest blocks were also established on 4 acres and different fruit plants including olive cultivated, he said adding that jojoba plants were grown over 45 acres in order to develop orchards and fruit farming in these areas.

In collaboration with local foundation, about 50,000 plants of different kinds including fruits and trees for shadow had also been provided to 20 villages, he added.

“We had installed a fertilizer plant to prepare fertilizer by using locust during current campaign against desert locust and distributed about 1500 bags of fertilizers among local farmers for producing organic agriculture products,” he added.

He said that PARC was also striving for mechanization of agriculture sector in these areas and helping the local farmers through providing them technical assistance.

2020 Onion Variety Trial Webinar and Onion Distribution

Please join us to discuss the results of the 2020 onion variety trial. This year included 16 short-day varieties, both yellow and red.

When: Tuesday, January 5th at 4:30 PM –
Where: Online, via Zoom –
What: How to select onion varieties and the variety trial results –

There will also be a drive-thru distribution of the onion varieties to conduct at-home taste testing. This is open to Maui commercial growers only. The drive-thru will be held next week on December 21, 22, and 23. Times and location will be shared with interested growers upon registration.

Register for the webinar and onion distribution here:

Download the flyer for more information.

Thank you!
Kylie Tavares
Edible Crops, Sustainable Agriculture, and Farm Food Safety Extension
University of Hawaii at Manoa, Dept. of Tropical Plant and Soil Sciences
Maui Agricultural Research and Extension Center
424 Mauna Place
Kula, HI 96790

Time to eat local

The Cougar Connection
By Natalie Clay –

Hawaii, despite its reputation as paradise, has its fair share of problems, one of which is food security. Currently, Hawaii only produces roughly 10-15% of its necessary food supply, while the remaining 85-90% is imported from across the ocean. Relying on the importation of food usually means consuming foods with more pesticides and genetic modifications that lack the nutrients of fresh produce. But most importantly, imported food leaves the islands vulnerable to tragedies that can disrupt shipping. Eating local food is a much safer option, supports local workers, and promotes land sustainability in a time where development is ever increasing. Unfortunately, Hawaii’s government has not been taking the serious action needed to improve this situation—therefore, it is time for the community to step in.

In the 2016 International Union for Conservation of Nature (IUCN) World Conservation Congress, Governor David Ige said, “I’m committed to doubling Hawaii’s food production by 2020,” endorsing many projects, startups, partnerships and funds to meet this goal. For Scott Enright, Chair of the Department of Agriculture, Ige had just sent the department into “hyper-drive”. However, Ige failed to meet this goal and has since extended the deadline to 2030. Even after the goal’s extension, Ige and the Hawaii Department of Agriculture (HDOA) have not been able to determine the status and progression of the goal. The Department of Agriculture doesn’t even have baseline information as to how much local food the state was producing in the first place, nor do they know how many farmers are producing food for a living. Lawmakers such as Rep. Matt Lopresti had been questioning the Governor’s and the HDOA’s ability to achieve this goal since the beginning. “So we’re going to double I don’t know, which is I don’t know times two. What’s the metric we’re going to be using?,” Lopresti said. It is clear that we must hold our government officials accountable to fulfilling their promises, especially for such an essential need.

It is important as citizens of a democracy to use our voices to promote change. The traditional ways of using that voice are still valid, such as writing letters to legislators, signing petitions, and speaking up at neighborhood board meetings. It must be made clear that in future elections, a candidate’s dedication to improving food security is a determining factor. Oftentimes the government does not hear the voices of the few, but the voices of the many, so it is important to encourage others to become active in this issue as well. If officials see that this issue is of utmost importance to the people of Hawaii, they will work harder at achieving their goals.

There are also ways that we as individuals can support the farmers who provide local food, particularly direct purchase of their produce. For those in the Hawaii Kai area, there are five farms right behind the Kaiser High School campus, some of which feature stands where you can purchase fresh fruits and vegetables. And all over the state there are community-supported agriculture (CSA) programs where you can order bags full of local produce. Some of these programs, such as Oahu Fresh, even offer the convenience of subscription and delivery. Local farms also struggle with the cost of importing fertilizer and animal feed, so you can also donate your food waste to farms that accept it, such as Keiki and Plow, one of the farms behind Kaiser. Any way you can support local food, from attending Agriculture Awareness Day at the capital, to buying Paniolo Cattle Co. beef at Safeway, helps to improve food security in our island community.

Promoting local food production is the best way to fight Hawaii’s struggle with food security. Since our government is struggling to improve the situation, we must take action ourselves. We can stress that Hawaii’s agriculture is necessary, and that officials who do not strive to improve its circumstances will not be elected again. Hawaii will soon be islands that know nothing other than importation, but if we support our local farmers, we can lead Hawaii into a greener, more fertile future.

Regeneration Is What We All Need Now

Civil Beat
By Vincent Mina

This is a story about the power of regeneration, and it starts where most everything starts when you’re a farmer: in the soil. If we want vitality in our bodies, we need it in our food. And if we want it in our food, we need it in our soil.

Healthy soil has an architecture, a web of microbial life. When that web is vital and intact, plants flourish and express themselves as complete proteins. Healthy plants are resilient and strong and able to fend off pests and diseases.

Our agricultural system is no different. I have been farming on Maui for 27 years. It has been a blessing and a challenge. As the saying goes, “If you want to make a million farming, start with two million.” We mahiai — farmers — are not ones to look for a free lunch. We produce that lunch.

According to a recent report from the U.S. Department of Agriculture, for every dollar American consumers spend on food, U.S. farmers and ranchers earn just 14.6 cents. This value marks a 17% decline since 2011, and the smallest portion of the American food dollar that farmers have received since the USDA began reporting these stats in 1993. The remaining 85.4 cents cover off-farm costs, including processing, wholesaling, distribution, marketing and retailing.

Most of us in Hawaii are very aware of the issues with farming in our islands today: Land costs that are too expensive. Land ownership that is too concentrated. Soil that has been exhausted and depleted by industrial sugarcane and pineapple farming. Prime agricultural land laying fallow until it’s plowed under for housing developments.

People looking to get by on the cheapest food they can find for themselves and their families. Billions of tons of food coming from elsewhere on cargo ships. People with a passion for farming who don’t get support. Extreme weather that is growing more extreme every year.

Heat. Wind. Floods. Drought. Invasive species. Now, a pandemic.

But this is a story about the power of regeneration. In Hawaii our climate allows us to grow an amazing variety of crops, and we can produce three harvests of seed a year.

Hawaii is a brilliant impresario, producing a vast web of biomass in which plants grow and grow and grow and stretch their roots deep into the earth. When that biomass is allowed to return to the soil in the form of organic matter, it feeds our soil’s microbial life.

The world is waking up to the need to protect our agricultural soils from erosion, but the story goes much deeper than that. We need to nourish our soil. When we feed its microbes, they proliferate. They break down organic biomass and turn it into humus, rich soil that nourishes life and produces truly healthy food.

Humus holds moisture and creates pathways for water to filter down into our precious aquifers. It sequesters carbon and moves the planet away from climate change. Today, we can all use more of a sense of humus.

The Hawaii Farmers Union United

As farmers, we also need to be nourished. We need the metaphorical organic biomass that will cause us to proliferate and thrive.

My grandparents left Sicily for Philadelphia when they were young. I left Philadelphia for Maui when I was 24 years old. I worked as a decorative painter and met an extraordinary Hawaiian woman, Irene, whose son Kekai was just 10 months old. Irene and I married and I adopted Kekai.

When Irene was pregnant with our daughter, Kahanulani, she started craving sunflower greens and coming home with bags and bags of them. So I started growing them and that was the launch of our farm, Kahanu Aina Greens. Irene and I worked side by side. Kekai, the hardest and most disciplined worker you could hope for and a boy full of passion for farming, joined in as soon as the farm began, when he was 10 years old.

As we farmed, I learned more about soil and the relationship between its health and the health of our bodies. I began attending conferences and met remarkable experts in the field of regeneration. I befriended those experts and from 1998 to 2014, Irene and I invited many of them to Maui for “Body and Soil” conferences that we produced under our nonprofit Maui Aloha Aina Association.

A decade ago, I was a founding member of the Hawaii chapter of the national Farmers Union, which was birthed out of our efforts with Maui Aloha Aina. Today the Hawaii Farmers Union United has a thousand members. We have 13 chapters across the islands. We are made up of Hawaii farmers, gardeners and food lovers on all islands who value local agricultural systems.

As a collective, we have a voice at the table. The growth in our clout and credibility has enabled us to work as a group with our county officials, our Legislature and the Department of Agriculture. At the national level, I worked with the Farmers Union to create the Regenerative Agriculture Local Food Committee, which I currently chair.

In the week ahead, we will celebrate 10 years of the HFUU with a major conference. And because COVID-19 has moved everything online, it has never been easier to attend. All are welcome.

There will be virtual farm tours. Virtual chefs’ demos. We will have over fifty presentations, workshops from global authorities as far away as Australia and Austria. We will cover many topics, including composting, earthworms, trellising, Korean natural farming, bees, hemp, mushrooms and much more.

We will have five keynote presentations from leaders including one of Hawaii’s most esteemed elders, Maui kupuna Sam Kaai; mycologist Paul Stamets; and regenerative farming expert Joel Salatin. Keynote discussions will focus on nature’s soil rebuilding process and on the relationship between the soil’s mycelium network, our gut biomes and COVID-19.

At the end of the conference, we will have a free three-hour benefit concert curated by Micah Nelson, son of Willie Nelson. Many great musicians have volunteered to perform in support of Hawaii farming: the Nelson ohana, Jack Johnson, Flea, George Kahumoku Jr., Makana, Michael McDonald, Pat Simmons Sr. and Jr., Mike Love, Paul Izak and others.

If you want to learn more about food and farming in Hawaii, right now there could be no better place to start. Everyone who registers will have access to all presentations for a year and all of the costs of registering for the conference go to support the HFUU and educational outreach.

Cover Crops

When I think about agriculture in our islands, I picture a Tesla that’s just sitting in the driveway. We are playing a very small game if we continue to rely on outside food supply to feed our local population.

And since this is the IDEAS section, I would like to share an idea of my own. It is an understanding and inspiration that has come from my own growth and experience as a farmer in Hawaii.

Our islands are perfectly situated to become a global leader in cover crop seed. Cover crops are crops that are grown in between production crops. They allow the soil to rest and nourish and feed its microbial life. They are the very essence of aloha aina.

Cover crop seed holds tremendous potential for Hawaii’s agricultural future. In our islands, we can grow three crops of cover crop seeds a year — seeds our farmers can use to build their own soils and seeds that we can sell around the world.

Across the globe and here in the islands, decades of industrial agriculture have withdrawn life from the soil. Big Ag has produced food cheaply by using chemicals that bypass and destroy the life in the soil instead of feeding it. The thinking has been short-term, not long-term. We can change that. The earth will collaborate and cooperate with us as long as we respect its natural laws and architecture.

As the understanding of the power of regeneration becomes more widespread, the demand for cover crop seed will only grow. And the demand is already huge.

I envision a cover crop seed industry that could be created on state agricultural lands in collaboration with the State of Hawaii, the University of Hawaii’s College of Tropical Agriculture Human Resources, the National Resource Conservation Service and the Hawaii Department of Agriculture.

I sit on the Board of Agriculture and I have been working to help bring this idea to fruition. It needs the support of government and the private sector. Farmers cultivate relationships with the earth and advocates cultivate relationships with people. I am committed to advocating and doing all I can in support of building a cover crop seed industry that honors Hawaii’s soil, that is founded on the principle of malama aina. I have not seen any better plan that protects our existing agricultural lands while utilizing the resources they represent.


As a regenerative farmer, I have a personal and ever–deepening relationship with the soil. It grows the food that nourishes my body and my body then works in service of the soil. Ultimately, one day I am going back to the soil. This relationship moves my spirit.

As a farmer, I let the soil decide what is going to happen. If I’m open and respectful, it teaches me. I act, I see the results. There are constant lessons. As a farmer, I haven’t arrived anywhere. I’m still learning. Nature continually forgives me and all of us.

This relationship is a primal relationship. For me, it is the only thing that gives reason to living and dying.

As humans we make plans and try to figure it all out. We focus on having, then doing, then being, rather than on being, then doing, then having. But we cannot control life.

Last year our family experienced a tragedy when Kekai passed away at 35. He was as healthy as a person can be and fell to his death in a hiking accident. Kekai, a Native mahiai who had farmed alongside us for 25 years, who sang songs in Hawaiian to the plants as he worked, who loved the family farm, who had planned to take over and continue it.

When he died, we shut down the farm for four months for the first time in its 26 years of operation. Burying one’s child is something a parent never gets over, and beyond what Kekai meant to the farm, we just miss him so very much.

After he passed, Kekai came to Irene in a dream and asked her to create a community cart. Irene described it to a neighbor, who built it. Now in honor of Kekai, we put the cart out in front of the farm every Monday, Wednesday and Friday.

We fill it with produce from the farm. Others in the community take as they need and give as they can. The cart operates from and with the energy of regeneration.

We feel Kekai is with us. Life never ends, it just changes form. This is the great lesson of regeneration. When you farm, that truth is no longer a philosophical abstraction. It is the energy of your daily life.

We invite you to join us this week at the conference and gather with us in the spirit of regeneration. Me ke aloha pumehana, with the warmest aloha.

Taro Leaf Blight—A Threat to Food Security

The Impact of Plant Disease on Food Security

by Davinder Singh, Danny Hunter, Robert Fullerton, Vincent Lebot, Mary Taylor, Tolo Iosefa, Tom Okpul, and Joy Tyson


Taro leaf blight (caused by the Oomycete Phytophthora colocasiae) is a disease of major importance in many regions of the world where taro is grown. Serious outbreaks of taro leaf blight in Samoa in 1993 and in the last few years in Cameroon, Ghana and Nigeria continue to demonstrate the devastating impact of this disease on the livelihoods and food security of small farmers and rural communities dependent on the crop. The spread of the disease to new geographical areas also poses a major threat to neighbouring countries and taro growing regions still free from the disease. Past research, particularly in the Pacific, has demonstrated that management measures such as chemical and cultural control are largely ineffective and that breeding for disease resistance is the most sustainable approach to manage the disease. Recently, the Pacific and South-east Asian regional taro networks have made excellent progress in developing cultivars resistant to taro leaf blight through enhanced utilization of taro genetic resources and close collaboration between farmers and researchers in breeding programs. These programs have secured vital taro genetic resources for future use. This paper provides an overview of the disease, its origin, distribution, biology, epidemiology, management and global impact. The paper will largely focus on breeding strategies to address the disease including challenges, opportunities and constraints. It also discusses how these breeding experiences and outputs can be scaled up to other geographical areas where the disease has been recently introduced or under threat of introduction.

Keywords: taro; Colocasia esculenta; taro leaf bight; Phytophthora colocasiae; resistance breeding; networks

1. Introduction

Taro (Colocasiaesculenta) a clonally propagated aroid, is grown largely in humid tropical areas of the world. The crop, first domesticated in South-east Asia, has continued to spread throughout the world and is now an important crop in Asia, the Pacific, Africa and the Caribbean [1]. It is the most important edible species of the monocotyledonous family Araceae. Almost all parts of a taro plant are utilized; corms are baked, roasted, or boiled as a source of carbohydrates, leaves are frequently consumed as a vegetable representing an important source of vitamins, and even petioles and flowers are consumed in certain parts of the world. Worldwide, taro ranks fourteenth among staple vegetable crops with about 12 million tonnes produced globally from about 2 million hectares with an average yield of 6 t/ha [2]. Most of the global taro production comes from developing countries, characterized by smallholder production systems relying on minimum external resource inputs. This makes this food crop very important for food security, especially among subsistence farmers in developing countries.

Worldwide, it is believed that crop diseases reduce agricultural productivity by more than 10%, equivalent to half a billion tonnes of food every year [3]. The epidemics associated with these diseases reduce food availability, increase food prices and pose a danger to rural livelihoods and regional food security. According to Fisher et al. [4] more than 600M people could be fed each year by halting the spread of fungal diseases in the world’s five most important crops alone. The overwhelming impact of plant diseases on human societies and food security is well illustrated by the effect of late blight disease of potato, caused by the pathogen Phytophthora infestans in Ireland during the 1840s, at a time when potato was an important staple food for the majority of the population. The disease was one of the factors that led to mass starvation, death and migration. There have been numerous other plant disease epidemics throughout agricultural history that have resulted in a major socio-economic impact; for example, the epidemics caused by coffee rust (Hemileia vastatrix) in Sri Lanka (1890s), brown spot of rice (Cochliobolusmiyabeanus) in India (1940s), wheat stem rust (Puccinia graminis) in north America (1960s), rubber leaf blight (Microcyclus ulei) in Latin America (1910s), and downy mildew of grape (Plasmopara viticola) in Europe (1880s) [5].

The important but neglected taro crop is no exception and is subject to significant losses from diseases and pests. Taro is affected by at least 10 major diseases and pests in different parts of the world [6]. Of the various taro diseases, taro leaf blight (TLB) caused by the fungus-like Oomycete Phytophthora colocasiae Raciborski (P. colocasiae) is of prime importance because it can reduce corm yield by up to 50% [7,8,9,10] and leaf yield by 95% in susceptible varieties [11]. TLB can also deteriorate corm quality [12,13]. In addition to corm yield losses that occur as a consequence of the reduced leaf area [7] in diseased plants, a corm rot caused by P. colocasiae may also occur [5]. Under some circumstances the disease invades harvested corms and causes heavy losses during storage [14].

Repeated outbreaks of TLB in the South Pacific, South-east Asia and recently in West Africa have signalled the urgency to find sustainable solutions to the disease. If uncontrolled, TLB poses a grave threat to food security and loss of crop genetic diversity, as well as impact on personal incomes and national economies. The devastation caused to the taro industry in Samoa (previously known as Western Samoa) as a result of the TLB outbreak in the early 1990s is an example of the destructive nature of the disease [15]. The disease caused serious economic hardship in rural areas, food insecurity and the loss of vital export earnings for the country. The introduction of TLB to the Caribbean in 2004 led to the annihilation of the taro crop in the Dominican Republic, Cuba and Puerto Rico [1]. Most recently TLB has been reported from West Africa in Cameroon [16], Nigeria [17] and Ghana [18] where it continues to decimate taro cultivation, and is impacting on the livelihoods and food security of rural communities. A number of other countries in West and Central Africa may face the same problem because the disease has the capacity to spread on taro planting material—the Oomycete has been reported to survive on planting tops for up to 3 weeks after harvest [19].

This paper provides an overview of TLB, its symptoms, origin, distribution, epidemiology, management and global impact. The paper will focus on breeding strategies to address the challenges presented by the disease, and how countries vulnerable to its advance can take advantage of the experiences and outputs of previous initiatives that have had to deal with its devastation.

2. History of Taro Leaf Blight Epidemics and Impacts

There has been limited documentation of the impact of TLB on countries and communities affected by the disease apart from the Pacific region. In most cases, wherever the disease has occurred in the Pacific, for example in Papua New Guinea, Solomon Islands, American Samoa and Samoa, the introduction of TLB has forced growers to abandon taro and grow other root crops [20].

It is believed that TLB has been present in the Pacific region since the early 1900s [21]. The disease was first recorded in Guam (1918) and later in Hawaii (1920). Prior to the arrival of the disease in Hawaii, it was thought that there were more than 300 different taro varieties but only a few have survived the impact of the disease [22]. Similarly, in Guam, more than 60% of known varieties are believed to have been lost as a consequence of the disease [23,24].

In Micronesia, TLB was reported during the Japanese occupation of Pohnpei [5]. Since then it is thought to have contributed to changes in the cropping system, which in turn has affected dietary patterns. Today, cassava has replaced taro as a major staple [25,26]. Most if not all the varieties that existed before the arrival of the Japanese are no longer present [22]. Taro now ranks behind yams, banana, rice, and breadfruit in Pohnpei [27].

In Papua New Guinea, outbreaks of TLB over the years are believed to have led to the decline in taro production and its displacement by sweet potato [28,29,30]. Most likely, the disease spread there from Indonesia during the Second World War. The outbreak in Bougainville was said to have contributed to the death of at least 3000 people [31]. Possibly, the occurrence of war forced communities to vacate their villages and take to forests, and the loss of taro to sustain them resulted in hunger and malnutrition [23,32]. More recently, severe epidemics occurred on the island of Manus in 1976 and in Milne Bay in 1988 completely destroying the crop on each occasion [20]. In Solomon Islands, the disease first appeared in the Shortland Islands in 1946 [33] and within a few years it swiftly spread to most provinces. The disease contributed to a decline in taro production throughout the country [5]. As in Papua New Guinea, disease outbreaks led to sweet potato rapidly replacing taro as the staple food crop [34].

The 1993-1994 epidemic of TLB in American Samoa and Samoa was catastrophic for taro production [35]. Before the disease introduction, taro was the main agricultural export of Samoa, but within six months there was little to trade [36]. Production fell from 0.4 million tonnes per year before the epidemic to less than 5 tonnes by the end of 1995 [37]. In 1993, the export value of taro for Samoa was US$3.5 million (about 58% of Samoa’s agricultural exports) but by 1994 the value had declined to less than US$60,000 [38] or about 0.5% of the 1993 export figure. Within two years from the start of outbreak in the Samoas, only 200 farmers were growing taro; these were farmers who had the resources to purchase fungicides. Most other growers abandoned the crop and shifted to alternative though less preferred crops such as Alocasia, Xanthosoma, breadfruit, banana, sweet potato and cassava. By 1994, supplies of taro on the local market were only 1% of the supplies of the previous year [39]. In response, both countries increased rice imports resulting in large trade imbalances.

In 2010, TLB spread to the West African nation of Cameroon where it caused harvest losses of up to 90% [16]. Not only are market prices very high for the little that is now available, there is a scarcity of planting material. The future is uncertain, as it is not clear if alternative food crops can fill the gap left by the demise of taro. Maize production in Cameroon has never met demand and plantains are usually very expensive. There is concern for food security and social unrest. The disease has spread rapidly to other countries in West Africa, including Nigeria and Ghana [17,18]. While it is too early to assess the impact of TLB on these countries, experience tells us that the disease has a potential to create a devastating cascade effect: reduction in food and household incomes, increased poverty and even starvation.

3. Diseases Symptoms

As its name implies, the most obvious and frequent symptom is a blight of the leaf lamina, but P. colocasiae also produces a postharvest rot of the corms. A petiole rot is also seen in susceptible varieties [37]. Early leaf infections often take place where rainfall, dew, or guttation droplets accumulate. Initial infections form water-soaked lesions that rapidly expand to form large brown spots [11]. The development of these lesions follows a characteristic day/night pattern. During the night, the lesions expand by developing a 3-5 mm wide water-soaked margin. This margin dries out during the day and a newer water–soaked zone forms the following night [40]. This results in a zonate pattern most easily seen when viewed from the bottom of leaf. Masses of sporangia form on the expanding margin of the lesion during the night, imparting a white powdery appearance to the lesions.

A conspicuous and characteristic feature of TLB lesions is the formation of droplets of amber, bright-orange, or reddish-brown exudate, oozing from the upper and lower surface of the water-soaked margins. These droplets dry out during the day to form crusty deposits on the surface of the lesion. It is common to observe lesions of different stages on the leaf. Lesions are also formed by sporangia that are splashed by irrigation, rain or wind-drive rain. As the lesion gets larger, the dead central area often breaks and falls out.

Infected petioles are uncommon, but occur in susceptible varieties. The infections start as small, brown, elongated spots. In wet weather, the spots can expand and soften until the petioles are broken by the weight of their leaves [41]. During dry weather the rate of lesion expansion generally slows and lesions may change colour, turning tan to brown with dark brown margins. In some resistant taro cultivars, the centre of lesions become papery and break apart, which gives a conspicuous “shot-hole” appearance [11]. Leaves of susceptible varieties collapse in about 20 days compared to 40 days for non-infected plants [42,43]. Therefore, photosynthesis is greatly reduced in susceptible plants, leading to progressively smaller leaves and corms.

Corm rots usually develop rapidly after harvest and entire corms can decay in 7–10 days. The rots usually start from areas damaged at harvest when the petiole bases and suckers are removed, especially during or after wet, warm conditions. In the early stages, the diseased tissue is light-brown, firm, and often has a distinct margin. In the advanced stages of corm rot, the decayed corm tissue may be invaded by Lasiodiplodia theobromae and turn black [14].

4. Origin, Dispersal and Distribution of Disease

Taro leaf blight was first described by Raciborski in 1900 [44] who named its causal pathogen P. colocasiae Racib. Information on the origin of P. colocasiae is limited [45] and the area of origin remains undefined [46]. Trujillo [9] speculated that the pathogen might have originated in South-east Asia, based on earlier reports of the disease in India. Ko [47] supported Asia as the centre of origin of P. colocasiae because of the coexistence of wild and cultivated varieties of taro in the region. According to Zentmyer [45], one of the indications of the centre of origin of an organism such as Phytophthora is the co-existence of A1 and A2 mating types with roughly an equal distribution in the same area. Based on this hypothesis, Ann et al. [48] screened about 800 isolates of P. colocasiae from Taiwan and all acted as A2 mating types, indicating that it is most likely not indigenous to Taiwan. Only the A1 mating type was previously reported from India [49] although recently A2 mating types from India have also been reported [50,51]. A further hypothesis of an Asian origin of P. colocasiae has recently come from China [46], where previously only A2 mating types were reported [52]. However, analysis of more than 200 isolates of P. colocasiae obtained from Hainan Island (an offshore island in the tropical region of southern China) recovered all three mating types, A0, A1 and A2 indicating that Hainan Island is likely to be inside the centre of origin of P. colocasiae from where it was dispersed. Fullerton & Tyson [53] reported only A2 mating type from Papua New Guinea, Hawaii and Guam, excluding these countries from the centre of origin of P. colocasiae. Tyson & Fullerton [51] further studied mating types of P. colocasiae from the Pacific region, South-east Asia and India and detected only A2 types, extending the A2 mating type list further to Indonesia, India, Philippines, Pohnpei, Thailand and Vietnam. Because of the apparently restricted distribution of the A1 mating type and the geographical separation from the areas in which it is found (Hainan Island, China and Northern India), the likelihood of the introduction of the A1 mating type to the Pacific region is considered to be relatively small [51].

Trujillo [9] postulated that the disease spread into the Pacific region by three different routes based on a possible South-east Asian origin for the pathogen. The first dispersal route is to Hawaii via the Philippines, the second from Taiwan to Micronesia via the Philippines and the third to Fiji via Papua New Guinea and Solomon Islands. At that time, TLB was reported to be present in Fiji but that record was based on a misidentification [5,23,40]. Nevertheless, the movement of TLB to Papua New Guinea and Solomon Islands would appear to be a separate route and is supported by only anecdotal evidence that the disease appeared after the Western Pacific Campaign of the Second World War [54]. Ooka [44] hypothesized that movement on the northern route went from Java to Taiwan, where the disease was reported in 1911. From Taiwan, it is believed to have moved to Japan and thence to Hawaii where it arrived in 1920 [21]. The disease was first recorded in the Philippines in 1916 and movement to Micronesia most likely occurred from there considering the disease was first recorded in Guam in 1918 [55]. There have been no studies on the distribution of mating types in American Samoa and Samoa that could indicate the likely sources of the pathogen, although it is widely speculated that the pathogen arrived in Samoa from Hawaii, probably through infected taro planting material [3].

The pathogen is believed to be distributed by means of vegetatively propagated material, and possibly by soil movement. The Oomycete is now widely distributed geographically over almost all continents including Asia (Bangladesh, Brunei, China, India, Indonesia, Irian Jaya, Japan, Korea, Malaysia, Peninsular Malaysia, Myanmar, Nepal, Pakistan, Philippines, Sri Lanka, Taiwan, Thailand), Africa (Cameroon, Equatorial Guinea, Ethiopia, Ghana, Nigeria, Seychelles), North America (USA), Central America and Caribbean (Brazil, Cuba, Dominican Republic, Puerto Rico, Trinidad and Tobago), South America (Argentina), Oceania (American Samoa, Guam, Northern Mariana Islands, Palau, Papua New Guinea, Samoa, Solomon Islands) [17,18,56,57]. Some of these reports have not been verified and need confirmation. For example, the disease in Fiji is clearly an invalid record [40].

5. Biology of the Pathogen

5.1. Host Range

Phytophthora colocasiae has limited host range [11]. The pathogen is known to infect primarily Colocasia spp. (C. esculenta, C. esculenta var. globulifer, C. antiquorum) and Alocasia macrorhiza (giant taro). Although Alocasia taro can be infected by the pathogen, the ability of the disease to become epidemic on this host is restricted by very low inoculum production [5]. Xanthosoma spp. (Xanthosoma saggittifolia) is immune [40]. Other reported hosts include Amorphophallus campanulatus (elephant-foot yam), Bougainvillea spectabilis (bougainvillea), Cantharanthus roseus (periwinkle), Dracontium polyphyllum (guapa), Hevea brasiliensis (rubber), Panax quinquefolius (American ginseng), Piper betle (betel), Piper nigrum (black pepper), Ricinis communis (castor bean) and Vinca rosea (periwinkle) [58]. Many of the records from these hosts, however, need to be confirmed.

5.2. Life Cycle

The disease cycle of P. colocasiae is dependent upon environmental factors (rainfall, humidity and temperature) and host genotype. The primary reproductive unit of the pathogen is the sporangium which requires free water to germinate. Although taro leaves have a waxy surface, the tiny droplets of water that accumulate on leaves provide sufficient moisture for sporangia to germinate. Under cooler conditions (close to 20 °C), the cytoplasm within each sporangium differentiates into 15–20 zoospores (Figure 1 and Figure 2), each oozing out through the terminal pore and moving through the water using their flagella. This is a rapid process and from the beginning of differentiation in the cytoplasm to zoospore release takes less than a minute. The zoospores settle onto the leaf surface within 10 min, lose their flagella and form a rounded cyst which soon germinates to form a germ tube. This mode of germination often referred as the “indirect mode” provides a strong ecological advantage to the pathogen as it generates up to a 15-fold increase in inoculum. New infections can be initiated within an hour of a sporangium being formed and P. colocasiae can continue sporulating and infecting during short periods of leaf wetness [40]. Under warmer conditions (about 25 °C), the sporangia germinate directly by germ tubes that can infect the leaves (Figure 1). This form of germination generally referred to as the “direct mode” is a slower process than zoospore production as it can take 5–6 h for a sporangium to germinate. The proportion of sporangia germinating directly is usually much lower than for those forming zoospores [59].
Agriculture 02 00182 g001 1024Figure 1. Sporangia of P. colocasiae germinating directly and also by productionof zoospores.

5.3. Infection Process and Conditions

Infection can occur on both surfaces of the leaf [11] and most infections occur between midnight and dawn [59]. Daytime infections occur only during continuously wet conditions. During infection, germ tubes developing from either sporangia or encysted zoospores penetrate the epidermis directly or enter via stomata. After penetration, the Oomycete spreads intercellularly through the mesophyll. First symptoms usually appear within 24 h and the rate of symptom development is greatest at temperatures in the range 25–30 °C under cloudy and/or showery conditions. At 35 °C symptom development is suppressed.

In wetland taro, sporangia can move with the water throughout a field and into adjacent paddies. The pathogen can also live for a time as mycelium in dead and dying plant tissues and in infected corms. During dry periods it can survive in the soil as encysted zoospores, or possibly as chlamydospores [60]. The life span of fungal mycelium in soils is usually short, surviving for less than five days. However, the encysted zoospores of P. colocasiae can endure for several months in the absence of a living host. Most sporangia in vegetative material (e.g., tops used for planting) seldom survive more than a few days though some have been shown to survive for up to 2 weeks [53]. Oospores and chlamydospores may operate as survival structures in infected plant tissues or sometimes in soils, but they are not frequently detected in the field (Figure 2) [11].

5.4. Genetic Variability and Heterothallism

P. colocasiae is a diploid heterothallic Oomycete, requiring opposite mating types (A1 and A2) for the formation of oospores [51]. Heterothallic species of Phytophthora readily produce oospores in pairings (intra- or inter-specific) of two compatible mating types [47] and different strains are likely to recombine and evolve rapidly depending on the frequency of A1 and A2 mating types. While oospore formation can be readily induced between opposite mating types in culture, there is no evidence that this event occurs regularly in nature.

The extent of genetic variability in P. colocasiae is unknown but in other Phytophthora species, sexual reproduction is associated with increased genetic variation, including increased variability in virulence and aggressiveness [53]. The capacity for sexual reproduction in P. colocasiae [46,49] has already been documented. Recently, Lebot et al. [61] studied isozyme variation among isolates of P. colocasiae originating from South-east Asia and the Pacific region and the results indicated that throughout this vast geographic region, TLB is caused by a plethora of distinct and genetically variable isolates. Variations occur within and among countries. Because P. colocasiae is diploid and heterothallic, different genetically variable isolates are likely to recombine and evolve depending on the frequency and occurrence of A1 and A2 mating types. Lebot et al. [61] have demonstrated that all zymotypes are unique to each country and this might be an indication of rapid evolution within isolated populations. In some countries, for example, Thailand, the high level of genetic diversity might indicate that both migration and sexual recombination play important roles in the population dynamics of P. colocasiae. However, Fullerton and Tyson [53] argued that although pathogenic variability may be inferred from a high degree of variability determined by enzyme or molecular analysis, this has not yet been demonstrated.

6. Disease Epidemiology

Favourable temperatures and regular periods of leaf wetness, particularly in the humid tropics promote TLB epidemics by favouring pathogen dispersal, infection, and disease development [62]. Outbreaks of the disease in new areas distant from known centres of infection probably result from the introduction of infected planting material. Within an infected area, the first lesions are due to infection from adjacent plants. Epidemics generally flourish when night temperatures are in the range 17–20 °C. The cool temperatures stimulate the release of infective zoospores, promoting multiple infections.

Taro leaves have waxy hydrophobic leaf cuticles, which assist the wash-off of sporangia and zoospores from the leaves into soil, or their splash onto other leaves and petioles, particularly the lower older ones. However, in the absence of regular rainfall, conditions favourable to re-infection occur on most nights ensuring regular cycling and survival on infected plants thus making it endemic. Under conditions of endemic survival, the distribution of infected plants in an area, and the severity of symptoms on those plants are generally irregular; while some plants become severely diseased with continuous night time sporulation and localised re-infection, others immediately adjacent may have little or no disease [53]. Generally, older leaves or younger leaves lower in the canopy are most severely affected because of a number of factors: a constant supply of inoculum deposited by runoff water or dew from above; a more conducive microclimate for the Oomycete lower in the canopy; and also because the less waxy cuticles of older leaves tolerates better adhesion of spore-carrying water drops [53]. Under normal circumstances large numbers of sporangia are also washed from lower leaves into the soil. While most of these lyse within the first few days, a small proportion develops thick walls, forming chlamydospores that are able to survive in soil for up to three months [60]. The importance of soil borne chlamydospores in the epidemiology of the disease has not been established but they could allow survival of the pathogen between crops [53]. In situations where vegetative material dies off because of drought or cold conditions, the pathogen most likely survives between seasons as vegetative mycelium in the infected corms [63]. In wetland taro production, the movement of paddy water carries these sporangia and zoospores among plants and between fields. Because growers propagate taro vegetatively, they often unknowingly transport P. colocasiae between fields and over long distances by the movement of infected planting material [11].

7. Disease Management Strategies

7.1. Cultural and Biological Control

A number of cultural methods have been recommended for the control of TLB disease. Individually each may be of limited benefit, but collectively they may play an important role in an integrated approach to disease management. The main cultural practices include removal of infected leaves during the early stages of disease development, wide spacing of plants to reduce disease spread, selection of sites surrounded by forest as a barrier to disease spread, isolation of new crops from those that are diseased, and the use of planting material free from disease [11,23,43]. Putter [59] showed that the removal of infected leaves was highly effective in controlling the disease in subsistence taro gardens, particularly when plots were relatively well separated from one another. This strategy can be effective when the disease is in an endemic phase with a relatively low and restricted disease incidence. In contrast, when the disease is in an epidemic phase, the removal of all leaves with lesions may lead to almost complete defoliation of the crop with consequent effects on yield [43]. This was the experience of growers in Samoa [64] where sanitation was largely abandoned as a disease management strategy. In some situations, intercropping of taro with other crops may help in reducing disease. Disease severity was found to be consistently higher in taro monocrops than in a taro/maize intercropping system [23,65]. Foliar application of biological control agents has some potential to protect taro crops from infection. For example, significant reductions in the numbers of infected leaves and disease severity were observed in taro plants sprayed with the fungus Trichoderma [66]. In Phichit plain near Phitsanulok, Thailand, some professional taro growers avoid serious TLB infections by planting during the dry season (V. Lebot, personal communication 2012) [67].

7.2. Chemical Control

Successful control of TLB is possible with chemicals even in high rainfall areas. A range of protectant and systemic fungicides have been found to provide effective control of TLB [7,11,43]. Mancozeb (e.g., Dithane M45), copper (e.g., copper oxychloride), metalaxyl (e.g., Ridomil Gold MZ) and phosphorus acid (e.g., Foschek) are amongst those most commonly recommended. Mancozeb and copper have protectant activity only. Metalaxyl and phosphorus acid are generally specific for Phytophthora diseases with the former prone to the development of resistance by the organism [53]. In contrast Jackson et al. [43] found that Mancozeb did not control the disease in Solomon Islands suggesting that results with chemical control can be variable. Similarly, Trujillo [68] reported that copper gave little control in Hawaii. In Samoa, a research program to investigate chemical control [3] recommended that phosphorus acid (Foschek), which was shown to give good control of TLB, should be alternated with Mancozeb to reduce costs and minimise the possibility of the Oomycete developing resistance. It was also observed that there were no significant differences between phosphorus acid formulations (Foschek, Agri-Fos 400 and Foli-R-Fos) for disease control. In some cases, soils may be drenched with approved products such as MetaStar or Ridomil as a pre-plant treatment and provide initial protection against TLB for 4–6 weeks [11].

The efficacy of fungicides is strongly governed by the severity of the disease at the time, and the prevailing weather conditions [53]. Generally, fungicides are most effective when disease incidence is low and timely applications reduce inoculum levels. When diseases enter an exponential phase, efficacy of disease control is reduced. Efficacy is also influenced by method of application, with motorised knapsack applications superior to conventional hydraulic machines [7,43], a fact related to improved coverage and speed of application especially in high rainfall situations. However, for most situations, the use of fungicides however applied is neither economically sustainable nor environmentally suitable.

7.3. Resistant Cultivars and Genetic Resources

The use of resistant varieties offers the most sustainable management strategy against TLB in most production systems. Resistance can be classified as either vertical or horizontal. Vertical resistance (VR), also referred to as monogenic resistance is generally controlled by one or few major genes and provides complete control against certain races of a pathogen [69]. It is often characterized by a hypersensitive reaction in the host. In a number of cases a gene-for-gene relationship has been demonstrated [70]. Subsequently, new pathogen races evolve that are able to attack previously resistant plants. For this reason, VR is often referred to as non-durable resistance [71].

The genetic control of VR against TLB may not be very complicated and simply inherited [72]. Although a number of genotypes have been shown to express a hypersensitive reaction when challenged by P. colocasiae, to date there is no evidence of breakdown of resistance by matching pathotypes [53]. However, it is an area little investigated. In contrast, horizontal resistance (HR) is controlled by a number of minor genes and does not involve a gene-for-gene relationship. It is considered effective against all races of a pathogen and has a reputation for durability, hence referred to as durable resistance. Unlike VR, this type of resistance does not give complete control but limits the spread of the pathogen within the plant and frequently reduces sporulation. The resistance mechanism in taro against TLB is considered to fall under the HR category based on several host-pathogen interaction models and genetic studies [69,70,73]. Because of predominant heterozygosity of taro genotypes, it is not easy to study the inheritance in a classical Mendelian fashion [74].

The physiological and biochemical mechanisms of resistance and host defence responses have not been studied in detail in the taro and P. colocasiae pathosystem [75]. Characteristic defence response in taro like many other host species likely includes systemic events through signalling and possibly constitutive and hydrolytic enzymes, enzyme inhibitors and phytoalexins. It was, however, established by Ho and Ramsden [75] that peroxidase enzymes play no vital role in the defence mechanisms of taro and proteinase inhibitors were the most important components for resistance to TLB. Recently Sharma et al. [76] employed suppressive subtractive hybridization, cDNA libraries, Northern blot analysis, high throughput DNA sequencing, and bioinformatics to identify the defence-related genes in taro induced by P. colocasiae infection. Using these genomic tools, two putative resistance genes and a transcription factor among the upregulated sequences were identified. There was a higher overall expression of these genes in TLB-resistant genotypes than in those susceptible to the disease.

Resistance in the majority of taro germplasm worldwide was previously considered to be limited globally. Recent evaluations, however, indicate that resistance in traditional cultivars exists in germplasm collections of several countries where TLB has been present for a long time, including the Philippines, Vietnam, Thailand, Malaysia, Indonesia and India [74]. Over twenty TLB-resistant taro varieties were also identified in germplasm from Palau. These genotypes also performed well in field trials in Hawaii [77,78] and many other Pacific Island countries. The genetic diversity of available resistance is, however, considered to be limited although germplasm from South-east Asia is considered to be more diverse than that in the Pacific [79,80,81]. The Centre for Pacific Crops and Trees (CePaCT formerly the Regional Germplasm Centre (RGC)) of the Secretariat of Pacific Community (SPC) maintains a collection of taro varieties with varying levels resistance to TLB. These varieties are the products of breeding programs in Hawaii, Papua New Guinea and Samoa. The CePaCT also has taro varieties from Asia, which have shown TLB resistance when evaluated in their countries of origin. In Hawaii, a new program collected almost 300 taro genotypes from Nepal, Thailand, Vietnam, Indonesia, Myanmar, China, Japan, and the Philippines, and from seven locations in Micronesia, Melanesia and Polynesia. Varying levels of resistance to TLB were noted [82]. Interestingly, 40% of 424 indigenous accessions at the Central Tuber Crop Research Institute of India were reported to show tolerance to TLB [83].

7.4. Breeding for Resistance to Taro Leaf Blight

Taro leaf blight control by breeding for resistance has proven to be an extremely cost-effective and environmentally acceptable approach [34,84,85,86]. The success of breeding for resistance against TLB depends on the availability of genetic resources and the type of resistance they confer [74,87]. The use of polygenic or HR is one of the most effective means to control TLB [8,86]. This breeding strategy involves the systematic selection of the resistant individuals from a population followed by recombination of the selected individuals to form a new population (recurrent selection). The main advantage of this strategy is its ability to accumulate minor resistance genes, which individually would confer minimal resistance [86], but together are likely to be additive and provide durable disease resistance. Because HR is not pathotype specific, failure to identify different pathotypes is not a limiting factor to the strategy [70,86]. A major challenge however, is the reliable identification of the least susceptible individuals in the population for use in the next cycle of inter-crossing. With HR breeding strategies, it is normal to generate many progenies of good agronomic quality differing widely in their degree of disease resistance. Such a range of material provides the opportunity to match the degree of resistance to the potential risk of disease [53]. Taro breeding programs have been implemented at a number of institutes worldwide, with those in Hawaii, Papua New Guinea, Samoa and Solomon Islands specifically focused on TLB.

The Papua New Guinea taro breeding program is based on a modified recurrent selection strategy and gives high priority to TLB resistance. Cycle-1 was developed in 1994 by crossing the resistant base population with superior (high yielding and tasting) local taro varieties [88]. Some partially superior genotypes were recovered from cycle-1 from among a majority that retained undesirable wild characteristics. Cycle-2 was created in 1996 by inter-crossing these partially superior genotypes. Three new varieties (NT 01, NT 02 and NT 03) were released from cycle-2 in 2001 [86,89], and one variety (NT 04) was released from cycle-3 by inter-crossing selected cycle-2 genotypes [8]. The development of these high-yielding varieties of taro has helped to reduce the threat of TLB in Papua New Guinea. The varieties performed well in farmers’ fields giving over 50% higher yields (about 9 t/ha) than the popular variety “Numkowec” (about 6 t/ha) used as a check [89]. These breeders’ lines have been widely adopted in many areas of Papua New Guinea [90]. Other elite hybrids (with high yield, acceptable palatability and resistance to TLB) have been identified post cycle-3 and are being considered for official release.

It is likely that those lines released from advanced cycles will be superior in their attributes, especially palatability, because of the polygenic breeding approach (accumulation of superior genes from cycle to cycle) adopted by the Papua New Guinea program. It appears from recent analyses that breeding selections have reached a plateau in terms of yield, and to make further genetic gains there is a need to cross local varieties with taro of different genetic backgrounds [91].

The goal of the Hawaii taro breeding program is to improve commercial taro for pest resistance, including TLB, and to increase genetic diversity. At the earlier stages of the program, a single source of TLB resistance from Palau was crossed with Hawaiian taro [68,92]. Later, multiple sources of resistance were introduced from Micronesia, Palau, Indonesia, Papua New Guinea, Thailand and Nepal. In cycle-1, crosses were made between commercial cultivars and introduced genotypes. The resulting hybrids were evaluated for desirable agronomic traits, and elite hybrids selected for the next cycle. The breeding program is based on two approaches. The first approach is similar to the breeding program in Papua New Guinea, and involves crossing commercial taro with TLB-resistant wild varieties from Thailand and Papua New Guinea. In this process, additional breeding (modified backcrossing or rigid selection through an extra generation) is needed to produce elite hybrids. This requires at least four years. The second approach is to cross commercial taro with TLB-resistant taro from Palau and Micronesia. In this process, elite types can be selected in the first year. Several new hybrids were produced including hybrids “99-6,” “99-7,” and “99-9”. These hybrids have greater tolerance to TLB, and yield 30% more than the industry standards, to which they are comparable in corm taste and colour [93].

The Samoan taro breeding program is different from that in Papua New Guinea and Hawaii. A participatory approach to breeding was adopted from the outset, which involved researchers, farmers and extension staff [29]. The Taro Improvement Program (TIP) at the University of the South Pacific began in early 1999. The aim was to bring together taro farmers via crop-focused participatory appraisals and provide them with options for improving production and managing TLB [29]. TIP made good progress and farmers evaluated and selected clones derived from crosses between local (Samoan) cultivars and those from Palau and the Federated States of Micronesia [29]. Later, to broaden the genetic diversity of the breeders’ lines, the program has made crosses using varieties from Asia to improve further TLB resistance whilst retaining the quality characteristics favoured by Samoans and the export market in New Zealand. To date, seven cycles of breeding have been completed. In 2009, the Ministry of Agriculture in Samoa released five TLB-resistant cultivars of which Samoa 1 and 2, identified from breeding cycle-5, are the most preferred for export [94,95].

The Vanuatu breeding program is based on combining genotypes from the two major genepools to establish a wide genetic base [96]. Elite cultivars for desired agronomic characteristics have been identified, based on an eco-geographic survey of the genetic variation existing in the region and systematic characterisation using morphological, agronomic and molecular characters. The resultant selections have been exchanged between participating countries: the Philippines, Vietnam, Thailand, Malaysia, Indonesia, Papua New Guinea and Vanuatu [79,97].

8. Role of Regional Networks for Controlling Taro Leaf Blight

After the serious outbreak of disease in Samoa in 1993, the occurrence of periodic epidemics in Papua New Guinea and Solomon Islands, and the threat of introduction of TLB to disease-free countries, the Pacific islands sought a regional collaborative approach to deal with the problem. No one country has sufficient resources to tackle the problem alone. There is much to be gained by countries participating in a regional network which facilitates germplasm sharing and enhancement, and keeps countries informed of activities in the region and outside. This provides a mechanism whereby collaboration can be fostered to achieve a more strategic approach to TLB control and taro improvement generally. It was identified that major constraints for taro breeding programs including TLB resistance breeding are the lack of knowledge of the genetic diversity in the cultivars, the limitations in access to and knowledge of additional sources of disease resistance as well as the absence of information on the potential agronomic and processing value of genotypes [74].

The crop network model was conceptualized with implementation of two regional collaborative projects. The first network, the AusAID-funded Taro Genetic Resources: Conservation and Utilization Network (TaroGen) re-activated the Papua New Guinea and Samoan TLB resistance breeding programs after a long dormant period, and linked them closely with other Pacific programs for the development of a core collection for Pacific taro and the safe sharing of virus-indexed breeders’ lines and traditional cultivars [86]. To link the Pacific with South-east Asia, a second network, the EU-funded Taro Network for South-east Asia and Oceania (TANSAO) was established [98]. Through the collaborative research that developed, there were notable achievements, and in less than a decade high yielding progenies resistant to TLB were developed.

Both TaroGen and TANSAO established networks incorporating local universities and research institutions, with regional and international organizations. Under TaroGen national collections (more than 2000 accessions) were assembled, characterized to identify a regional core representing the genetic diversity of taro in the region, and conserved [80,99]. Under TANSAO, a core sample was made that captured much of the genetic diversity from South-east Asia. Both networks successfully improved taro quality and resistance to TLB. They also achieved significant outputs in diagnostics for taro viruses, as well as initiated the establishment of regional genebanks in Fiji (SPC) and Indonesia (LIPI). The SPC genebank is now an international hub for the conservation and distribution of taro in Asia and the Pacific.

The success of these two networks laid the foundation for the genesis of a new initiative, the International Network for Edible Aroids (INEA) which aims to link all the major taro genepools and promote the interchange of taro genetic resources worldwide (www.ediblearoids.org) [100]. In addition to many food security goals, this new network holds the potential to manage TLB, especially in West Africa where extensive epidemics have been reported recently.

9. Way Forward for Mitigating Impact of TLB on Food Security

Taro leaf blight has been a particularly destructive disease in the Pacific and South-east Asia over many decades and has now reached West Africa. Food security of smallholder farmers has been threatened in all these regions, and in some cases economies put at risk, as the disease is difficult to manage by conventional means. The only solution has come through resistance breeding, but the difficulty in this approach has been a lack of a worldwide coordinated strategy. However, in recent years the success of regional interventions has given hope and shown that collaboration between countries is possible and has great merit. This success has largely come from the result of the networks built under TaroGen and TANSAO [91]. Genetic resources were collected and shared and used to breed for resistance. The key lessons learnt from TaroGen and TANSAO collaboration were: the need to use modern biotechnologies to solve crop improvement problems, linking countries, regional institutions and universities with centres of excellence outside the regions that specialise in DNA fingerprinting, virus indexing and conservation; that farmers must be involved in taro breeding from the outset; and that effective and efficient project co-ordination is required, ensuring interaction among national programs, other partners and funding agencies [101]. These are the strategies now being implemented by INEA to use taro and other edible aroids to build a model to improve clonally propagated crops of the tropics. INEA is a timely intervention, coming at a critical time for farmers in West Africa who are now suffering the consequences from the inadvertent introduction of TLB to that continent. The devastation caused there is a salient reminder of the potential of P. colocasiae to undermine food security and the need for lasting solutions.


We thank Emil Adams and Fred Brooks for kindly providing the diagrams presented in this review.


Rao, R.; Hunter, D.; Eyzaguirre, P.; Matthews, P. Ethnobotany and global diversity of taro. In The Global Diversity of Taro: Ethnobotany and Conservation; Ramanatha Rao, V., Matthews, P.J., Ezyaguire, P.B., Hunter, D., Eds.; Bioversity International: Rome, Italy, 2010; pp. 2–5. [Google Scholar]

FAOSTAT. FAO Statistical Database, 2010. FAOSTAT Web site. Available online: http://faostat.fao.org/ (accessed on 15 June 2012).

Hunter, D.; Iosefa, T. Chemical control of taro leaf blight. In Proceedings of Taro Leaf Blight Seminar, Alafua, Western Samoa, 22–26 November, 1993; South Pacific Commission: Noumea, New Caledonia, 1996; pp. 26–27. [Google Scholar]

Fisher, M.C.; Henk, D.A.; Briggs, C.J.; Brownstein, J.S.; Madoff, L.C.; McGraw, S.L.; Gurr, S.J. Emerging fungal threats to animal, plant and ecosystem health. Nature 2012, 484, 186–194. [Google Scholar]

Brunt, J.; Hunter, D.; Delp, C. A Bibliography of Taro Leaf Blight; Secretariat of the Pacific Community: Noumea, New Caledonia, 2001; pp. 1–10. [Google Scholar]

Kohler, F.; Pellegrin, F.; Jackson, G.V.H.; MacKenzie, E. Taro. In Diseases of Cultivated Crops in Pacific Island Countries; Secretariat of the Pacific Community: Noumea, New Caledonia, 1997. [Google Scholar]

Jackson, G.V.H. Taro leaf bligh. In Pest Advisory Leaflet; the Plant Protection Service
of the Secretariat of the Pacific Community: Noumea, New Caledonia, 1999; Volume No. 3, p. 2. [Google Scholar]

Singh, D.; Guaf, J.; Okpul, T.; Wiles, G.; Hunter, D. Taro (Colocasia esculenta) variety release recommendations for Papua New Guinea based on multi-location trials. N. Z. J. Crop Horticult. Sci. 2006, 34, 163–171. [Google Scholar] [CrossRef]

Trujillo, E.E. Diseases of the Genus Colocasia in the Pacific Area and their control. In Proceedings of the International Symposium on Tropical Root Crops, St Augustine, Trinidad, 2–8 April 1967; 2.

Trujillo, E.E.; Aragaki, M. Taro blight and its control. Hawaii Farm Sci. 1964, 13, 11–13. [Google Scholar]

Nelson, S.; Brooks, F.; Teves, G. Taro Leaf Blight in Hawaii; Plant Disease Bulletin No. PD-71. University of Hawaii: Manoa, HI, USA, 2011. [Google Scholar]

Paiki, F.A. Symptoms of taro leaf blight disease (Phytophthora colocasiae) and relationship with yield components in Biak, Irian Jaya. Sci. New Guin. 1996, 21, 153–157. [Google Scholar]

Sar, S.A.; Wayi, B.M.; Ghodake, R.D. Review of research in Papua New Guinea for sustainable production of taro (Colocasia esculenta). Trop. Agr. Trinidad 1998, 75, 134–138. [Google Scholar]

Jackson, G.V.H.; Gollifer, D.E. Storage rots of taro, Colocasia esculenta, in the British Solomon Island. Ann. Appl. Biol. 1975, 80, 217–230. [Google Scholar] [CrossRef]

Chan, E.; Milne, M.; Fleming, E. The causes and consequences of taro leaf blight in Samoa and the implications for trade patterns in taro in the South Pacific region. Trop. Agr. Trinidad 1998, 75, 93–98. [Google Scholar]

Guarino, L. Taro leaf blight in Cameroon? 2010. Available online: http://agro.biodiver.se/2010/07/taro-leaf-blight-in-cameroon/ (accessed on 15 May 2012).

Bandyopadhyay, R.; Sharma, K.; Onyeka, T.J.; Aregbesola, A.; Kumar, P.L. First report of taro (Colocasia esculenta) leaf blight caused by Phytophthora colocasiae in Nigeria. Plant Dis. 2011, 95, 618. [Google Scholar]

Omane, E.; Oduro, K.A.; Cornelius, E.W.; Opoku, I.Y.; Akrofi, A.Y.; Sharma, K.; Kumar, P.L.; Bandyopadhyay, R. First report of leaf blight of taro (Colocasia esculenta) caused by Phytophthora colocasiae in Ghana. Plant Dis. 2012, 96, 292. [Google Scholar]

Jackson, G.V.H. Taro leaf bligh. In Advisory Leaflet No. 3; South Pacific Commission: Noumea, New Caledonia, 1977; p. 4. [Google Scholar]

Jackson, G.V.H. Brief summary of situation in the region and comments on available assistance for long-term regional projects on taro leaf blight control. In Proceedings of Taro Leaf Blight Seminar, Alafua, Western Samoa, 22–26 November 1993; South Pacific Commission: Noumea, New Caledonia, 1996; pp. 71–74. [Google Scholar]

Carpenter, C.W. Report of the plant pathologist. Rept. Hawaii Agric. Expt. Stn. 1920, 49–54. [Google Scholar]

Trujillo, E.E. Taro leaf blight research in the American Pacific. Agr. Dev. Am. Pac. Bull. 1996, 1, 1–3. [Google Scholar]

Hunter, D.; Pouono, K.; Semisi, S. The impact of taro leaf blight in the Pacific Islands with special reference to Samoa. J. S. Pac. Agr. 1998, 5, 44–56. [Google Scholar]

Wall, G.C. Life after blight: The current taro leaf blight status on Guam. In Proceedings of Taro Leaf Blight Seminar, Alafua, Western Samoa, 22-26 November 1993; South Pacific Commission: Noumea, New Caledonia, 1996; pp. 39–40. [Google Scholar]

Barrau, J. Subsistence Agriculture in Polynesia and Micronesia; Technical Bulletin No. 223; Bernie, P. Bishop Museum: Hawaii, HI, USA, 1961. [Google Scholar]

Jackson, G.V.H. Taro Leaf Blight Control Strategies; First Consultancy Mission Report for AusAID/MAFFM/WSFSP; International Development Support Services Pty Ltd.: Melbourne, Australia, 1996; p. 34. [Google Scholar]

Primo, A. Colocasia taro on Pohnpei Island. In Proceedings of the Sustainable Taro Culture for the Pacific Conference, Honolulu, Hawaii, 24–25 September 1992; Hawaii Institute of Tropical Agriculture and Human Resources: Manoa, HI, USA, 1993; pp. 6–8. [Google Scholar]

Bourke, R.M. The decline of taro and taro irrigation in Papua New Guinea. In Irrigated Taro (Colocasia esculenta) in the Indo-Pacific: Biological, Historical and Social Perspectives; Spriggs, M., Addison, D., Matthews, P., Eds.; Senri Ethnological Studies 78, National Museum of Ethnology: Osaka, Japan, 2012; pp. 255–264. [Google Scholar]

Hunter, D.; Iosefa, T.; Delp, C.; Fonoti, P. Beyond taro leaf blight: A participatory approach for plant breeding and selection for taro improvement in Samoa. In Proceedings of the International Symposium on Participatory Plant Breeding and Participatory Plant Genetic Resource Enhancement, Pokhara, Nepal, 1–5 May 2000; CIAT: Cali, Colombia, 2001; pp. 219–227. [Google Scholar]

Singh, D.; Okpul, T.; Iramu, E.; Wagih, M.; Sivan, P. Breeding taro for food security in PNG. In Proceedings of the Papua New Guinea Food and Nutrition 2000 Conference, Lae, Papua New Guinea, 26–30 June 2000; pp. 749–751.

Putter, C.A.J. Taro Blight (Phytophthora colocasiae) in Western Samoa; FAO Mission Report No. TCP/SAM/2353; FAO: Italy, Rome, 1993.

Packard, J.C. The Bougainville Taro Blight; University of Hawaii: Honolulu, HI, USA, 1975; p. 144. [Google Scholar]

Liloqula, R.; Saelea, J.; Levela, H. The taro breeding program in Solomon Islands. In Proceedings of Taro Leaf Blight Seminar, Alafua, Western Samoa, 22–26 November 1993; South Pacific Commission: Noumea, New Caledonia, 1996; pp. 143–147. [Google Scholar]

Iramu, E. Breeding Taro (Colocasia esculenta) for Leaf Blight Resistance. Master’s Thesis, University of Technology, Lae, Papua New Guinea, 2003. [Google Scholar]

Gurr, P. The taro leaf blight situation in American Samoa. In Proceedings of Taro Leaf Blight Seminar, Alafua, Western Samoa, 22–26 November 1993; South Pacific Commission: Noumea, New Caledonia, 1996; pp. 35–38. [Google Scholar]

Semisi, S.T. Taro leaf blight disease, Phytophthora colocasiae, in Western Samoa. In Proceedings of Taro Leaf Blight Seminar, Alafua, Western Samoa, 22-26 November 1993; South Pacific Commission: Noumea, New Caledonia, 1996; pp. 63–68. [Google Scholar]

Brooks, F.E. Detached-leaf bioassay for evaluating taro resistance to Phytophthora colocasiae. Plant Dis. 2008, 92, 126–131. [Google Scholar] [CrossRef]

Putter, C.A.J. Taro Blight (Phytophthora colocasiae) in Western Samoa; Technical Report for Western Samoa Farming Systems Project; Ministry of Agriculture, Forestry, Fisheries and Meteorology; MAFFM: Apia, Samoa, 1996; p. 8.
Paulson, D.D.; Rogers, S. Maintaining subsistence security in Western Samoa. Geoforum 1997, 28, 173–187. [Google Scholar]

Fullerton, R.; Tyson, J. Overview of leaf diseases of taro. In Proceedings of Taro Pathology and Breeding Workshop, Alafua Campus, Samoa, 5–7 November 2001; pp. 4–7.

Brooks, F.E. Taro leaf blight. Plant Health Instr 2005. [Google Scholar]

Jackson, G.V.H.; Gollifer, D.E. Disease and pest problems of taro (Colocasia esculenta L. Schott) in the British Solomon Islands. Trop. Pest Manag 1975, 21, 45–53. [Google Scholar]

Jackson, G.V.H.; Gollifer, D.E.; Newhook, F.J. Studies on the taro leaf blight fungus Phytophthora colocasiae in Solomon Islands: Control by fungicides and spacing. Ann. Appl. Biol. 1980, 96, 1–10. [Google Scholar]

Ooka, J.J. Taro diseases. In Proceedings of Taking Taro into the 1990s: A Taro Conference, Hilo, HI, USA, 17 August 1989; University of Hawaii: Honolulu, HI, USA, 1990; pp. 51–59. [Google Scholar]

Zentmyer, G.A. Origin and distribution of four species of Phytophthora. Trans. Brit. Mycol. Soc. 1988, 91, 367–378. [Google Scholar]

Zhang, K.M.; Zheng, F.C.; Li, Y.D.; Ann, P.J.; Ko, W.H. Isolates of Phytophthora colocasiae from Hainan Island in China: Evidence suggesting an Asian origin of this species. Mycologia 1994, 86, 108–112. [Google Scholar] [CrossRef]

Ko, W.H. Mating-type distribution of Phytophthora colocasiae on the island of Hawaii. Mycologia 1979, 71, 434–437. [Google Scholar] [CrossRef]

Ann, P.J.; Kao, C.W.; Ko, W.H. Mating-type distribution of Phytophthora colocasiae in Taiwan. Mycopathologia 1986, 93, 193–194. [Google Scholar] [CrossRef]

Narula, K.L.; Mehrotra, R.S. Occurrence of A1 mating type of Phytophthora colocasiae. Ind. Phytopathol. 1981, 33, 603–604. [Google Scholar]

Misra, R.S.; Mishra, A.K.; Sharma, K.; Jeeva, M.L.; Hegde, V. Characterisation of Phytophthora colocasiae isolates associated with leaf blight of taro in India. Arch. Phytopathol. Plant Prot. 2011, 44, 581–591. [Google Scholar] [CrossRef]

Tyson, J.L.; Fullerton, R.A. Mating types of Phytophthora colocasiae from the Pacific region, India and South-east Asia. Australas. Plant Dis. Notes 2007, 2, 111–112. [Google Scholar] [CrossRef]

Ho, H.H.; Hu, Y.N.; Zhuang, W.Y.; Liang, Z.R. Mating types of heterothallic species of Phytophthora in China. Acta Mycol. Sinica 1983, 2, 187–191. [Google Scholar]

Fullerton, R.; Tyson, J. The biology of Phytophthora colocasiae and implication for its management and control. In Proceedings of the Third Taro Symposium, Nadi, Fiji Islands, 21-23 May 2003; Secretariat of the Pacific Community: Noumea, New Caledonia, 2004; pp. 107–111. [Google Scholar]

Oliver, D. Bougainville: A Personal History; University Press of Hawaii: Honolulu, HI, USA, 1973. [Google Scholar]

Weston, W.H., Jr. Report on plant diseases in Guam. In Guam Agricultural Experiment Station Report; Guam Agricultural Experiment Station: Guam, 1918; pp. 45–62. [Google Scholar]

Commonwealth Mycological Insti

Misra, R.S.; Sharma, K.; Mishra, A.K. Phytophthora leaf blight of taro (Colocasia esculenta)—A review. The Asian Australas. J. Plant Sci. Biotechnol. 2008, 2, 55–63. [Google Scholar]

Phytophthora Species in the Environment and Nursery Settings New Pest Response Guidelines; Technical Report; USDA, Animal and Plant Health Inspection Services (APHIS): Riverdale, MD, USA, 2010.

Putter, C.A.J. Phenology and Epidemiology of Phytophthora colocasiae Racib. on Taro in the East West Province, Papua New Guinea. Ph.D. Thesis, University of PNG, Papua New Guinea, 1976. [Google Scholar]

Quitugua, R.J.; Trujillo, E.E. Survival of Phytophthora colocasiae in field soil at various temperatures and water matric potentials. Plant Dis. 1998, 82, 203–207. [Google Scholar]
Lebot, V.; Herail, C.; Pardales, J.; Gunua, T.; Prana, M.; Thongjiem, M.; Viet, N. Isozyme and RAPD variation among Phytophthora colocasiae isolates from South-east Asia and the Pacific. Plant Pathol. 2003, 52, 303–313. [Google Scholar] [CrossRef]

Thankappan, M. Leaf blight of taro-a review. J. Root Crop. 1985, 11, 1–8. [Google Scholar]

Butler, E.J.; Kulkarni, G.S. Colocasia blight caused by Phytophthora colocasiae Rac. Mem. Dep. Agr. Ind. Bot. Ser. 1913, 5, 233–261. [Google Scholar]

Adams, E. Farmers use both chemical and cultural methods to control TLB. IRETA S. Pac. Agr. News 1999, 16, 7. [Google Scholar]

Amosa, F.; Wati, P. Effects of Taro/Maize Intercropping Systems on the Incidence of and Severity of Taro Leaf Blight; Technical Report in 1995 Annual Research Report; University of the South Pacific: Apia, Samoa, 1997; pp. 1–2. [Google Scholar]

Palomar, M.K.; Mangaoang, Y.C.; Palermo, V.G.; Escuadra, G.E.; Posas, M.B. Biocontrol of root crop diseases through microbial antagonism. In Proceedings of the 4th Asia-Pacific Biotechnology Congress and 30th Annual Convention of the PSM, Laguna, Philippines, 16-18 May 2001; pp. 56–62.

Lebot, V. CIRAD, Port Vila, Vanuatu. Personal communication, 2012. [Google Scholar]

Trujillo, E.E. Taro leaf blight in Micronesia and Hawaii. In Proceedings of Taro Leaf Blight Seminar, Alafua, Western Samoa, 22–26 November 1993; South Pacific Commission: Noumea, New Caledonia, 1996; pp. 41–43. [Google Scholar]

Singh, D.; Okpul, T.; Gunua, T.; Hunter, D. Inheritance studies in taro cultivar “Bangkok” for resistance to taro leaf blight. J. S. Pac. Agr. 2001, 8, 22–25. [Google Scholar]

Robinson, R.A. Aroids. In Return to Resistance; AgAccess: Davis, CA, USA, 1996; pp. 237–238. [Google Scholar]

Singh, D.; Okpul, T.; Hunter, D. Taro leaf blight control strategies: Disease resistance. In Proceedings of Taro Pathology and Breeding Workshop, Alafua Campus, Samoa, 5–7 November 2001; SPC: Suva, Fiji, 2002; pp. 44–45. [Google Scholar]

Patel, M.Z.; Saelea, J.; Jackson, G.V.H. Breeding strategies for controlling diseases of taro in Solomon Islands. In Proceedings of the Sixth symposium of the International Society for Tropical Root Crops, Lima, Peru, 21-26 February 1983; International Potato Center: Lima, Peru, 1984; pp. 143–149. [Google Scholar]

Ivancic, A.; Kokoa, P.; Simin, A.; Gunua, T. Mendelian studies of resistance to taro leaf blight. In Proceedings of the Second Taro Symposium, Manokwari, Indonesia, 23–24 November 1994; Cenderawasih University: Manokwari, Indonesia, 1996; pp. 97–100. [Google Scholar]

Ivancic, A.; Lebot, V. The Genetics and Breeding of Taro; Editions Quae: Montpellier, France, 2000. [Google Scholar]

Ho, P.K.; Ramsden, L. Mechanisms of taro resistance to leaf blight. Trop. Agr. Trinidad 1998, 75, 39–44. [Google Scholar]

Sharma, K.; Mishra, A.; Misra, R. Identification and characterization of differentially expressed genes in the resistance reaction in taro infected with Phytophthora colocasiae. Mol. Biol. Rep. 2009, 36, 1291–1297. [Google Scholar] [CrossRef]

Greenough, D.R.; Trujillo, E.E.; Wall, G. Effects of Nitrogen, Calcium, and/or Potassium Nutrition on the Resistance and/or Susceptibility of Polynesian Taros, Colocasia esculenta, to the Taro Leaf Blight, Caused by the Fungus Phytophthora colocasiae; Technical Report in ADAP Project Accomplishment Report, Year 8–9; Agricultural Development in the American Pacific Project: Honolulu, HI, USA, 1996; pp. 19–25.

Trujillo, E.; Wall, G.; Greenough, D.; Tilialo, R. Effects of Nitrogen, Calcium, and/or Potassium Nutrition on the Resistance and/or Susceptibility of Polynesian Taros, Colocasia esculenta, to the Taro Leaf Blight, Caused by the Fungus Phytophthora colocasiae; Technical Report in ADAP Project Accomplishment Report, Year 8–9; Agricultural Development in the American Pacific Project: Honolulu, HI, USA, 1997; pp. 27–40.

Lebot, V.; Prana, M.S.; Kreike, N.; van Eck, H.; Pardales, J.; Okpul, T.; Gendua, T.; Thongkiem, M.; Hue, H.; Viet, N.; et al. Characterisation of taro (Colocasia esculenta (L.) Schott) genetic resources in South-east Asia and Oceania. Genet. Resour. Crop Evolut. 2004, 51, 381–392. [Google Scholar]

Mace, E.S.; Mathur, P.N.; Izquierdo, L.; Hunter, D.; Taylor, M.B.; Singh, D.; DeLacy, I.H.; Jackson, G.V.H.; Godwin, I.D. Rationalisation of taro germplasm collections in the Pacific island region using SSR markers. Plant Genet. Resour. 2006, 4, 210–220. [Google Scholar] [CrossRef]

Singh, D.; Mace, E.S.; Godwin, I.D.; Mathur, P.N.; Okpul, T.; Taylor, M.; Hunter, D.; Kambuou, R.; Rao, V.R.; Jackson, G. Assessment and rationalization of genetic diversity of Papua New Guinea taro (Colocasia esculenta) using SSR DNA fingerprinting. Genet. Resour. Crop Evolut. 2008, 55, 811–822. [Google Scholar] [CrossRef]

Taro Research by College of Tropical Agriculture and Human Resources (CTAHR); Background Paper, CTAHR Cooperative Extension Service, University of Hawaii: Manoa, HI, USA, 2009; 1–37.

Edison, S.; Sreekumari, M.T.; Pillai, S.V.; Sheela, M.N. Diversity and genetic resources of taro in India. In Proceedings of Third Taro Symposium, Nadi, Fiji Islands, 21-23 May 2003; Secretariat of the Pacific Community: Noumea, New Caledonia, 2004; pp. 85–88. [Google Scholar]

Dey, T.K.; Ali, M.S.; Bhuiyan, M.K.R.; Siddique, A.M. Screening of Colocasia esculenta (L.) Schott lines to leaf blight. J. Root Crop. 1993, 19, 62–65. [Google Scholar]

Gollifer, D.E.; Brown, J.F. Phytophthora leaf blight of Colocasia esculenta in the British Solomon Islands. Papua New Guinea Agr. J. 1974, 25, 6–11. [Google Scholar]

Singh, D.; Hunter, D.; Iosefa, T.; Fonoti, P.; Okpul, T.; Delp, C. Improving taro production in the South Pacific through breeding and selection. In The Global Diversity of Taro: Ethnobotany and Conservation; Ramanatha Rao, V., Matthews, P.J., Ezyaguire, P.B., Hunter, D., Eds.; Bioversity International: Rome, Italy, 2010; pp. 168–184. [Google Scholar]

Iramu, E.T.; Akanda, S.; Wagih, M.E.; Singh, D.; Fullerton, R.A. Evaluation of methods for screening taro (Colocasia esculenta) genotypes for resistance to leaf blight caused by Phytophthora colocasiae. Papua New Guinea J. Agr. For. 2004, 47, 37–44. [Google Scholar]

Okpul, T.; Ivancic, A.; Simin, A. Evaluation of leaf blight resistant taro (Colocasia esculenta) varieties for Bubia, Morobe province, Papua New Guine. Papua New Guinea J. Agr. For. Fish. 1997, 40, 13–18. [Google Scholar]

Okpul, T.; Singh, D.; Wagih, M.; Wiles, G.; Hunter, D. Improved Taro Varieties with Resistance to Taro Leaf Blight for Papua New Guinean Farmers; NARI Technical Bulletin Series No. 3; National Agricultural Research Institute: Lae, Papua New Guinea, 2002. [Google Scholar]

Guaf, J.; Komolong, B. Impact assessment of three Taro (Colocasia esculenta) varieties in the Morobe Province, Papua New Guinea. Papua New Guin. J. Agr. For. Fish. 2006, 49, 19–27. [Google Scholar]

Yalu, A.; Singh, D.; Yadav, S. Taro Improvement and Development in Papua New Guinea—A Success Story; Technical Report; Asia Pacific Association of Agricultural Research Institutions: Bangkok, Thailand, 2009; pp. 1–37.
Trujillo, E.E.; Menezes, T.D.; Cavaletto, C.G.; Shimabuku, R.; Fukuda, S.K. Promising New Taro Cultivars with Resistance to Taro Leaf Blight: “Pa‘lehua”, “Pa‘akala”, and “Pauakea”; Technical Report New Plants for Hawaii NPH-7; University of Hawaii: Manoa, HI, USA, 2002.

Cho, J.J.; Yamakawa, R.A.; Hollyer, J. Hawaiian Kalo, past and future. In Sustainable Agriculture; SCM-1; University of Hawaii: Honolulu, HI, USA, 2007; pp. 1–8. [Google Scholar]

Iosefa, T.; Taylor, M.; Hunter, D.; Tuia, V.S. Supporting farmers’ access to the global gene pool and participatory selection in taro in the Pacific. In Community Biodiversity Management: Promoting Resilience and the Conservation of Plant Genetic Resources; De Boef, W.S., Peroni, N., Subedi, A., Thijssen, M.H., Eds.; Earthscan Publications: London, UK, 2012. [Google Scholar]

Iosefa, T.; Taylor, M.; Hunter, D.; Tuia, V.S. The taro improvement program in Samoa: sharing genetic resources through networking. In FAO RAP-NIAS Plant Genetic Resources in Asia and the Pacific: Impacts and Future Directions; FAO Regional Office for Asia and the Pacific: Bangkok, Thailand, 2012; pp. 25–40. [Google Scholar]

Lebot, V.; Aradhya, K.M. Isozyme variation in taro (Colocasia esculenta (L.) Schott.) in Asia and Oceania. Euphytica 1991, 56, 55–66. [Google Scholar]

Lebot, V.; Ivancic, A.; Abraham, K. The geographical distribution of allelic diversity, a practical means
of preserving and using minor root crop genetic resources. Exp. Agr. 2005, 41, 475–489. [Google Scholar]

Lebot, V. A taro network for South-east Asia and Oceania (TANSAO). SABRAO J. 1997, 29, 61–62. [Google Scholar]

Taylor, M.; Hunter, D.; Rao, V.R.; Jackson, G.V.H.; Sivan, P.; Guarino, L. Taro collecting and conservation in the Pacific region. In The Global Diversity of Taro: Ethnobotany and Conservation; Ramanatha Rao, V., Matthews, P.J., Ezyaguire, P.B., Hunter, D., Eds.; Bioversity International: Rome, Italy, 2010; pp. 150–167. [Google Scholar]

International Network for Edible Aroids. Available online: www.ediblearoids.org (accessed on 9 June 2012).
Lebot, V.; Simeoni, P.; Jackson, G. Networking with food crops: a new approach in the Pacific. In Plant Genetic Resources in the Pacific: Towards Regional Cooperation in Conservation and Management; Wells, K.F., Eldridge, K.G., Eds.; Australian Centre for International Agricultural Research: Canberra, Australia, 2001; pp. 82–85. [Google Scholar]

© 2012 by the authors; licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).