Fight continues to contain potato diseases

By JAMES LARAKI of NARI

Efforts by the National Agricultural Research Institute (NARI) to address the potato late blight (PLB) disease which completely wiped out the industry in Papua New Guinea in 2003 is continuing with the evaluation of PLB-resistant varieties sourced from the International Potato Centre (CIP) in Peru.

 Okapa harvest… Farmers harvesting potato in a NARI evaluation trial in Okapa, Eastern Highlands. – Pictures by DAVID MINEMBA

The disease, caused by the fungus, Phtopthora infastans, remains a concern to the potato farmers, especially in the highlands where the crop is usually grown.
The fungus is a specialised pathogen of potato and, to a lesser extent, tomato which comes from the same plant family.
Late blight is an extremely destructive fungal disease of potatoes.
The fungus attacks both tubers and foliage at any stage of development and is capable of rapid development and spread.
It was responsible for the devastating Irish potato famine of the 1840s and has continued to be important to the present.
Since the Irish famine, late blight became the most-studied potato disease in the world.
Intense studies on the disease led to successful development of control methods such as the chemical fungicides and late blight-resistant varieties.
Late blight is still a terrible crop killer, striking fear into the hearts of potato growers worldwide. Late blight destroys an estimated 15% of the annual potato crop worldwide; in developing countries alone the disease costs about US$3.25 billion per year in lost production.
The late blight fungus has the power to appear out-of-the-blue and wipe out countries'’ entire potato industries in a few weeks.
In 2003, it destroyed the potato industry in PNG, then worth around K25 million.
Previously free of the disease, the country was one of the world's few remaining safe havens for growing potato.
It is believed to have come across from the neighboring Irian Jaya, Indonesia.
Within a short period of time, the fungus spread fast throughout the country after it was first discovered in Surunki, Enga province in March, leaving a trail of destruction.
Yield losses caused many smallholders, who relied on potato as a valuable cash crop, to withdraw from production, leading to an increase in potato prices in the country.
Some breakthrough has been made to control PLB using fungicides, however, the extra input is a burden to smallholder growers and identifying suitable varieties looks to be the long-lasting solution to revive the potato industry.
Subsistence farmers, making up the majority of farmers in PNG, rely on potato as an important cash and food source.
For some smallholders it was their main crop until the 2003 outbreak.
NARI PLB project leader, David Minemba, told visitors to the NARI Highlands Regional Centre field day recently in Tambul, Western Highlands that his team is working around the clock to identify suitable varieties to deal with the PLB problem.

E2 field…Potato field at NARI Tambul of the E2 clone, one of the CIP clones that is expected to be released by NARI to the farming communities next month.

Minemba noted that the famous Sequoia variety is still susceptible to PLB and only well-to-do farmers were growing this variety as they had the capacity to meet the additional input required. The devastating late blight disease has prevented smallholder farmers in PNG from growing the popular potato variety Sequoia.
Seed potatoes, fertiliser and fungicides are expensive and weekly fungicide sprays are now needed to make this variety productive.
Fresh Produce Development Agency, with input from NARI, has been successful in laying the foundation for rebuilding PNG potato industry through the delivery of supplies of quality seed and through village extension worker training activities, which have involved some 2, 500 smallholders.
However, at present, potato production in PNG is generally limited to a relatively small number of commercial growers who have access to land, backpack sprayers, chemicals, and seed potatoes and are growing the highly-susceptible cultivar Sequoia.
Minemba says the average farming households cannot affordable to grow the traditional variety as it is expensive and the PLB project is trying to identify resistant varieties with these farmers in mind.
Potato is not only a commercial crop but is also a source of food next to kaukau (sweet potato), particularly in the high altitude highlands region of PNG where the choice of staple food is limited.
NARI sourced 36 CIP clones in 2003 and evaluation work has been undertaken at various locations where the crop is grown.
Out of these, 12 clones were identified and further evaluation has been undertaken under the PLB project supported by the Australian Centre for International Agricultural Research Centre (ACIAR).
The objectives of the project are to introduce, multiply, evaluate and deploy late blight-resistant clonal material into PNG and to develop safe, cost-effective integrated late blight management strategies for existing and new potato cultivars and ultimately to rehabilitate potato production for smallholders.
This evaluation process has further identified four varieties to be promising and further evaluation work has been undertaken throughout potato-growing areas in PNG.
Minemba says with the farmers’ desire for the crop and food security in mind, his team will soon recommend two of the four promising varieties to the farming communities while work on PLB continues.
The institute is expected to officially release the two promising varieties to the farming community next month during its Agricultural Innovations Show with the aim of assisting smallholder farmers to grow the famous crop once again.