Press Release
Research Programme on Potato Late Blight Disease
5th May 2004
The Potato late blight disease was first observed in Papua New Guinea in the Sirunki area of the Enga Province in January 2003. The disease is caused by the fungus Phytophthora infestans.
Within weeks, the problem was seen to be serious and reports from farmers reached the Enga Fresh Food Marketing Depot, Fresh Produce Development Company (FPDC), and the National Agricultural Research Institute (NARI). Staff from NARI and FPDC went to the outbreak area and collected samples for identification and the initial fears were confirmed – potato late blight had finally reached Papua New Guinea .
The disease was causing a major problem to all crops of potato in the outbreak area. By the end of February, it had spread to the Western Highlands Province and by April to all Highland Provinces. The disease affects all varieties of potatoes and many other species in the potato family including tomato and capsicums. Some varieties exhibit tolerance to the disease. Unfortunately for PNG, the variety which has proved to be the most productive, the variety Sequoia, has no tolerance, and has been very severely affected.
The disease appeared and spread very quickly. Generally, the crop was totally destroyed within a few days of the farmer noticing the first symptoms. So quickly in fact, that many farmers thought their crops had been destroyed by frost. Within about two months of the disease being discovered, production of potatoes in the main growing areas had ceased.
Unfortunately the disease is well suited to the climate of the highlands of Papua New Guinea. The climate is cool and humid throughout the year. In the past this climate has favoured potato growing where farmers have been able to grow the crop throughout the year. In many potato growing areas of the world, potatoes are not grown through the winter. This results in a reduction in the disease. Also, hot dry summers do not favour the disease. This means that the disease is only active for a limited time during the growth of the crop.
In PNG, the crop can be grown throughout the year, and conditions for the spread of the disease occur throughout the year. The disease has a short generation cycle of about five days. This together with the favourable conditions for infection and growth of the fungus has meant that spread was extremely rapid.
Fungicides are used elsewhere in the world to control the disease. The most readily available fungicides in the highlands at the time of the outbreak were copper based fungicides used for the control of coffee leaf rust. Field trials were run by both NARI scientists and several local potato farmers. These fungicides gave a reasonable degree of control when sprayed every five to seven days. Control though depended on achieving very good leaf cover to protect the leaves from infection. It also depended on commencing the spray programme as soon as possible after the new crop emerged after planting.
At the time of the outbreak, the Fresh Produce Development Company had seed of a number of varieties they had been testing. These were planted to assess their tolerance to the disease under PNG conditions. They were grown at a number of sites. The variety Knox generally had very little infection, while the varieties Spunta, Kennebec and Sebago had considerable less disease than Sequoia. In past trials, Knox had not cropped very heavily. So while it had little disease, its cropping capabilities were considered suspect. Also, this is no longer a commercial variety in Australia, so certified seed is not available. Sebago and Kennebec are common commercial varieties in Australia and certified seed would be available. A decision was made to cease producing Sequoia seed and change to Sebago which has cropped nearly as well as Sequoia in past trials. Kennebec has generally yielded somewhat less than Sebago, so this variety was ruled out for general use.
Following the outbreak, submissions were sent to various funding organizations to help implement a control programme for the disease. This comprised an Integrated Pest Management approach including suitable tolerant varieties, cultural practices, fungicides and application techniques. The Australian Agency for International Development (AusAID) responded quickly by granting approximately Kina 363,000 to cover the operational expenses during the first year of the proposed programme. This has helped the initial work to progress. This support has also allowed adequate time to organise technical and funding support to more fully develop the later stages of this programme. We would like to thank very sincerely AusAID for their quick and crucial response at the critical stage.
Work carried out to date include multi-location variety trials with the four better varieties identified in the initial screening and fungicide trials looking at a wider range of possible fungicides. Fungicides containing “chlorothalonil” have been found to be much more effective than the copper based fungicides initially tested. It has been found though, that good control using standard backpack type knapsack spray pumps is difficult. Further work in this area is needed to be able to provide better options for farmers.
Obtaining seed of a wider variety of potatoes has proved more difficult than expected. Material is held in overseas gene banks as tissue culture, which has had to be multiplied before despatch under tight quarantine to PNG. So far thirty-six varieties have been received from the International Potato Centre in Peru , and are being multiplied for field trials. These varieties have shown good levels of tolerance to the disease in Kenya where climatic conditions are similar to the highlands of PNG. A range of commercial varieties has been received from Toolangi in Victoria . Both of these sets of varieties will have to be assessed in PNG for tolerance to the disease as well as evaluating other agronomic and consumer traits.