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Temperature adaptation and fungicide sensitivity in Macrophomina phaseolina, the causal agent of charcoal rot on soybean and dry bean

Viviana Ortiz Londono: Michigan State University

<div>Charcoal rot caused by <em>Macrophomina phaseolina</em> can significantly reduce yield and seed quality in soybean and dry bean, especially under hot and drought conditions. Consequently, production is affected mainly in tropical and subtropical regions. However, the incidence of charcoal rot in soybean has recently been increasing in the northern US, in which pathogen temperature adaptation may be involved. To address this, genomes of 96 <em>M. phaseolina</em> isolates, collected from soybean and dry bean grown in the northern and southern US, Puerto Rico and Colombia, were sequenced to 23X coverage using a 150 base-pair paired-end strategy on the Illumina HiSeq 4000 platform. Mycelial dry weight at 15ºC relative to 35ºC was used to evaluate the influence of temperature on fungal growth. Some isolates from the northern US grew faster at 15ºC than isolates from the southern US and Colombia. To assess fungicide sensitivity, relative mycelial growth of <em>M. phaseolina</em> isolates challenged against boscalid (SDHI), iprodione (dicarboximide) and prothioconazole (DMI) was used to determine EC<sub>50</sub> values. Most isolates were sensitive to boscalid, iprodione and prothioconazole, with EC<sub>50</sub> distributions means of 1.55, 0.92 and 0.24, and ranges of 0.15 – 28.31, 0.63 – 1.49 and 0.16 - 1.17 µg ml<sup>-1</sup>, respectively. Combined phenotypic and genomic approaches and population genomics are being used to identify genomic regions and candidate genes involved in temperature adaptation and fungicide sensitivity.</div>