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Transmission of Magnaporthiopsis maydis from maize seeds to seedlings

Gary Munkvold: Iowa State University

<div><em>Magnaporthiopsis maydis </em>(syn.<em> Harpophora maydis</em>) is a seedborne fungus that causes late wilt of maize, a disease that is economically important in several parts of the world, but does not occur in the Americas. Potential introduction of <em>M. maydis</em> into the United States is considered a serious threat to U.S. agriculture because of its probable impact on maize production and trade. Although the fungus is known to be seedborne, there is little information regarding the occurrence of seed-to-seedling transmission. In this study, maize seeds were inoculated using a water-restriction method, which resulted in external seed contamination. Approximately 1,000 inoculated seeds were planted in individual pots in a restricted access growth chamber. After 4 weeks, coleoptile and mesocotyl tissues were dissected and surface-disinfested, and individually subjected to PCR analysis. <em>M. maydis</em> was detected by PCR in mesocotyl tissues of 6 (0.94%) of 639 seedlings that emerged from inoculated seeds. All seedlings from noninoculated seeds tested negative. Although disease symptoms could not be observed during the short duration of the experiment, and we did not attempt to re-isolate the fungus from seedlings, these results indicate that <em>M. maydis</em> can potentially be seed transmitted, suggesting the continued need for careful phytosanitary measures to prevent its movement with seeds. Further work is needed to clarify the risk of seed transmission from naturally contaminated seeds.</div>