Source: CIMMYT E-News, vol 2 no. 11, November 2005

Knowing the Enemy: Foliar Blight

CIMMYT and partners in Nepal have identified new sources of genetic resistance to a disease that makes wheat plants looks as though they have been through a drought. The symptoms of foliar blight result from fungal infections, either spot blotch or the less well-known but related tan spot. These pathogens dry the wheat plant and shrivel grain. In the warm areas of South Asia, that appearance can lead farmers to blame drought rather than an infection. By “knowing the enemy,” as CIMMYT partner Ram Sharma puts it, it is easier to win the fight against the disease.

CIMMYT pathologist Etienne Duveiller and Sharma, who have both done work on the pathogens, have found an effective method to select for resistance: finding wheat with a heavy grain weight, early maturity, and resistance to both pathogens. Wheat that carries these three traits together makes for wheat with higher resistance. Through regional collaborative trials in South Asia, they have bred and identified wheat lines that look promising. While better than anything previously seen in the area, these wheats can still suffer up to 35% yield losses—and have a huge impact on resource poor farmers who grow their wheat for food, as most do in Nepal.

When the temperature soars to 26-28°C, however, no wheat can resist the disease. This is why it is so important to find wheat that matures early to avoid the abrupt rise in temperature accompanied by hot winds in late March and April. This becomes difficult as most farmers in the region are delayed planting wheat as they wait for their rice harvest to finish and the paddies to dry up.

In addition to genetic resistance, solutions can come in the form of good management. Surface seeding, when seed is broadcast on the mud directly after the rice harvest, allows earlier planting and gives the wheat crop a jump start on the heat. Crop rotation and soil nutrients are important because healthy soils help the crop resist the disease. Also, Duveiller and Sharma have found that wheat is better able to withstand the disease with proper soil moisture.

The CIMMYT-Nepal team expects that these new sources of resistance, coupled with good management practices, will limit the destructiveness of this disease. They know it can be done—foliar blight has already been substantially reduced in areas of South Asia such as Bangladesh through better wheat varieties. The challenge is to sustain progressive control of this threat across the warm wheat growing areas of South Asia.