Charcoal rot (Macrophomina phaseolina) resistance and the effects of water stress on disease development in sorghum

In three field experiments, plants subjected to post‐flowering water stress and inoculated with Macrophomina phaseolina had greater development of charcoal rot symptoms than did inoculated plants not subjected to water stress. Two sorghum genotypes (B35‐6 and SC265‐14E) were found to be consistently more resistant to M. phaseolina , an assessment that was facilitated by the use of appropriate soil moisture conditions at the time of greatest plant susceptibility to charcoal rot. In addition, an isolate of M. phaseolina originally isolated from a sorghum genotype with resistance to charcoal rot caused greater symptom development than did two other isolates originally obtained from sorghum genotypes susceptible to charcoal rot.