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Detection of threatening emerging pathogens in maize and wheat seed : phytosanitary challenges, regulations and solutions

Monica Mezzalama: CIMMYT

<div>The <em>Maize chlorotic mottle virus</em> (MCMV) responsible for maize lethal necrosis in East Africa since 2011 and <em>Magnaporthe oryzae</em> <em>Triticum </em>(MoT), responsible for wheat blast in the tropical parts of South America since 1985 and in Bangladesh since 2016, have emerged as serious threat to global maize and wheat production, respectively. Seed transmission was suspected to be the mechanism of intercontinental spread of both these pathogens. Reliable testing procedures for pathogen detection in seed lots have become a high priority for enforcing effective phytosanitary controls during seed exchanges. In this study we present development of seed testing methods and regulatory procedures for declaring seed lots and germplasm meant for international exchange free from MCMV and MoT for commercial and research purposes. Enzyme-linked immunosorbent assay (ELISA) for MCMV in maize and a polymerase chain reaction (PCR) with MoT specific primers in wheat were found to be the most reliable and cost-effective methods for pathogen detection in seed lots. Challenges to diagnostic test development due limited knowledge on rate and mode of seed transmission of MCMV, and occurrence of different MoT pathotypes will be presented.</div>

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