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Wheat blast has emerged as a major threat to wheat production in South America. Although originally restricted to Brazil, the disease has since been observed in the neighboring countries of Argentina, Bolivia, and Paraguay and recently the pathogen, Magnaporthe oryzae Triticum pathotype, was isolated from infected wheat in Bangladesh. There is growing concern that the pathogen may continue to spread to other parts of the world, including the United States, where several M. oryzae pathotypes are endemic. M. oryzae pathotypes are morphologically indistinguishable and, therefore, must be characterized genotypically. Symptoms of wheat blast include bleaching of the head, which closely resembles the symptoms of Fusarium head blight, further complicating efforts to monitor for the presence of the pathogen in the field. We used a genomics-based approach to identify molecular markers unique to the Triticum pathotype of M. oryzae. One of these markers, MoT3, was selected for the development of a polymerase chain reaction (PCR)-based diagnostic assay that was evaluated for specificity using DNA from 284 M. oryzae isolates collected from a diverse array of host species. Conventional PCR primers were designed to amplify a 361-bp product, and the protocol consistently amplified from as little as 0.1 ng of purified DNA. The specificity of the MoT3-based assay was also evaluated using Fusarium spp. DNA, from which no amplicons were detected. [ABSTRACT FROM AUTHOR]

Wheat blast, caused by the Triticum pathotype of Magnaporthe oryzae, is an emerging disease considered to be a limiting factor to wheat production in various countries. Given the importance of wheat blast as a high-consequence plant disease, weather-based infection models were used to estimate the probabilities of M. oryzae Triticum establishment and wheat blast outbreaks in the United States. The models identified significant disease risk in some areas. With the threshold levels used, the models predicted that the climate was adequate for maintaining M. oryzae Triticum populations in 40% of winter wheat production areas of the United States. Disease outbreak threshold levels were only reached in 25% of the country. In Louisiana, Mississippi, and Florida, the probability of years suitable for outbreaks was greater than 70%. The models generated in this study should provide the foundation for more advanced models in the future, and the results reported could be used to prioritize research efforts regarding the biology of M. oryzae Triticum and the epidemiology of the wheat blast disease. [ABSTRACT FROM AUTHOR]