Location: Foreign Disease-weed Science ResearchTitle: Genomics-based marker discovery and diagnostic assay development for wheat blast Author
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2016
Publication Date: 9/19/2016
Citation: Pieck, M.L., Ruck, A.L., Farman, M.L., Peterson, G.L., Stack, J.P., Valent, B., Pedley, K.F. 2017. Genomics-based marker discovery and diagnostic assay development for wheat blast. Plant Disease. 101:103-109. Interpretive Summary: Wheat blast disease, caused by the fungal pathogen Magnaporthe oryzae, has emerged as a major threat to wheat production in South America. While originally restricted to Brazil the disease has since been observed in the neighboring countries of Argentina, Bolivia, and Paraguay and there is growing concern that pathogenic strains from South America may spread to other parts of the world including the United States. Isolates of the pathogen are sub-classified into strains or pathotypes based on the host plant they infect. The Triticum pathotype, which infects wheat and is responsible for wheat blast, is visually indistinguishable from other pathotypes and must therefore, be characterized by molecular DNA methodologies. The objective of this work was to develop a diagnostic assay that could differentiate between the South American strains that cause wheat blast from other pathotypes. We identified and tested molecular markers to determine their suitability for assay development and one marker, MoT3, was found to be a reliable marker specific for the Triticum pathotype. This assay will enable a rapid characterization of infected wheat samples during future discoveries and will provide essential information to researchers and regulatory agencies that will guide mitigation and eradication efforts.
Technical Abstract: Wheat blast has emerged as a major threat to wheat production in South America. While originally restricted to Brazil the disease has since been observed in the neighboring countries of Argentina, Bolivia, and Paraguay and there is growing concern that the pathogen, Magnaporthe oryzae Triticum pathotype, may 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 must therefore be characterized genotypically. Symptoms of wheat blast include bleaching of the head that closely resemble 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 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 394 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.