Wheat blast, first identified in Brazil in 1985 and widespread throughout South America, deforms grain, causing it to bleach, shrivel and shrink. At its worst, the fast-moving disease can decimate a crop, leading to the urgent need for a multi-pronged approach to fight it.
The recent appearance of the disease, which is caused by the plant fungus pathogenMagnaporthe oryzae, in six districts in southern Bangladesh is estimated to have affected 15% of the country’s total wheat growing area of 436,000 hectares (1.08 million acres).
“We need to fight this disease on various fronts – both in the short and long term,” said Etienne Duveiller, principal scientist and wheat pathologist with CIMMYT, adding that strategies include preventing the distribution of infected seed, sowing seed at designated optimal times, introducing foliar spray of triazole fungicides and developing disease-resilient seed.
“It’s paramount that infected seeds are identified and that seeds are sown at the best time to avoid rains at the sensitive stage when wheat plants develop the spike where grains form, but we’ve also been working to identify resistant genetic materials – germplasm – for use in developing new varieties, a vital part of the longer term fight against the disease,” he said.
CIMMYT scientists are working with national agriculture programs on this work, setting up germplasm exchanges and testing genotypes in hot spot areas where the disease occurs, Duveiller said, adding that a smallholder farmer in one of the worst-hit areas said he expected to harvest 80% less wheat as a result of the disease. The problem compounds over time because farmers keep seed and replant it in subsequent years.
Scientists believe wheat blast spreads by various means, including airborne distribution, from crops planted in rotation with wheat and sexual hybridization.
“We’re not sure what the potential scale of wheat blast spread might be because we’re still trying to understand how it survives from wheat crop to wheat crop, we urgently need investments to understand it,” said Hans Braun, director of CIMMYT’s Global Wheat Program.
“It takes only a few days from the first symptoms occurring until major damage is caused by the fungus,” he said. “This short window makes chemical interventions difficult and prophylactic application of fungicides is too expensive for smallholder farmers. Breeding resistant varieties is the best and possibly the only option to control the disease in the long term.”