Association of dhurrin levels and post-flowering non-senescence with resistance to stalk rot pathogens in Sorghum bicolor

Sorghum ( Sorghum bicolor (L.) Moench) is a diverse C4 crop used for feed, food and grain- or juice-based bioethanol, with potential for lignocellulosic biofuels. Sorghum is inherently drought tolerant, but it is vulnerable to stalk rots caused by Fusarium thapsinum and Macrophomina phaseolina , especially during water stress. Post-flowering non-senescent lines ( Stay-green ), associated with drought and stalk rot resistance, tend to have higher levels of the cyanogenic glycoside, dhurrin, than post-flowering senescent sorghums. The goal of this study was to identify grain sorghum lines with stalk rot resistance, but with low levels of dhurrin for grain and forage uses. Stay-green and senescent lines were screened for response to the two stalk pathogens. Greenhouse and field assessments indicated that four lines had increased resistance: Plant Introduction (PI) 267,379, PI 533882, PI 534053 and PI 534133. When dhurrin levels of greenhouse-grown flag-leaves were assessed using HPLC, only PI 267379 and the senescent check BTx623 had significantly less dhurrin than the Stay-green check BTx642. For field-grown flag-leaves, PI 267379, PI 533882 and BTx623 had significantly lower dhurrin levels than BTx642. Field-grown lines were visually scored post-anthesis for percent senescent leaves to indicate degree of leaf greenness. The PI 533882 and PI 534133 had percent senescence ratings similar to or lower than that of BTx642 while PI 267379 and PI 534053 had ratings significantly higher. Among lines exhibiting increased resistance to stalk rot, PI 267379 and PI 533882 show promise for developing grain and forage sorghums with stalk rot resistance.