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Field response of near-isogenic brown midrib sorghum lines to Fusarium thapsinum and effects of controlled water deficit on stalk rot disease

Deanna Funnell-Harris: Wheat, Sorghum, and Forage Research Unit, USDA-ARS

<div>To increase digestibility of sorghum [<em>Sorghum bicolor</em> (L.) Moench] biomass for ruminant livestock and lignocellulosic biofuels production, near-isogenic <em>brown midrib</em> (<em>bmr</em>) lines, <em>bmr6, bmr12</em> and <em>bmr6 bmr12</em> double mutant in backgrounds RTx430 and Wheatland were developed. Compared with wild-type, <em>bmr </em>lines have reduced lignin, altered lignin composition and altered phenolic metabolite levels due to mutations in monolignol pathway genes whose products synthesize lignin subunits. In previous greenhouse assays, <em>bmr </em>lines were not more susceptible, or were more resistant, to Fusarium stalk rot caused by <em>Fusarium thapsinum</em>, compared to wild-type. This destructive disease can result in lodging under high temperature or drought conditions. To determine if greenhouse results applied to field environments, <em>bmr</em> and near-isogenic wild-type plants were inoculated with <em>F. thapsinum </em>at irrigated and dryland sites. Mean lesion lengths of most <em>bmr</em> lines were similar to wild-type; <em>bmr6 bmr12</em> plants had smaller lesions than corresponding wild-type under irrigation (P=0.03). To assess <em>F. thapsinum </em>virulence under drought condition, wild-type plants were inoculated in the greenhouse with adequate or deficient water regimes. Mean lesion lengths were greater on water-stressed plants than those on plants adequately watered (P=0.01). Development of this screen provides a way to identify sorghum germplasm with increased resistance or tolerance to Fusarium stalk rot under drought conditions.</div>