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Wheat Blast: unveiling epidemiological aspects

Mauricio Fernandes: Embrapa Wheat

<div><span>Wheat blast is an emerging disease in South America and Asia caused by the Triticum pathotype of <i>Magnaporthe oryzae</i> (MoT). Wheat blast is a serious disease capable of causing severe losses, especially during warm and humid weather conditions. Here, we report a weather based model to predict wheat blast outbreaks. Specifically, uncommonly humid and warm weather during a 60-day period preceding wheat heading is considered key drivers of inoculum build up and airborne spores from regional inoculum sources in the surroundings. A day favoring infection was conditioned to rules relating temperature and relative humidity. Successful daily infection was conditioned to the inoculum size and density of spores in the air. The risk model has been successfully applied to Brazil and Bangladesh conditions. Although MoT has not yet been reported in North America, the closely related <i>M. oryzae</i> Lolium pathotype (MoL) is commonly found in wheat growing regions and could pose a threat under certain environmental conditions. Multifactorial experiments were conducted under controlled conditions to evaluate the effects of different combinations of temperature, relative humidity duration, inoculum concentration, and growth stage. Results showed that the odds of a spike becoming infected was significantly (P < 0.05) greater when inoculated at early heading than at full head emergence, anthesis, or early grain fill. However, once infected, the rate of blast severity increase per unit increased in high RH duration was significantly greater (P < 0.05) when infections occurred at Feekes 10.5.1 (anthesis) or 10.5.4 than between Feekes 10.1 and 10.5. The rate of increase in severity per hour increase in 100% RH was significantly greater at 25 and 30C than at 20C. These results are invaluable for ongoing efforts to assess the risk posted by MoL to US wheat. </span></div>

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