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

Authors: Funnell-Harris, Deanna; Sattler, Scott; O`Neill, Patrick; Toy, John; Bernhardson, Lois; Kilts, Mark; Khasin, Maya

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2022
Publication Date: 2/24/2022
Citation: Funnell-Harris, D.L., Sattler, S.E., Oneill, P.M., Toy, J.J., Bernhardson, L.F., Kilts, M., Khasin, M. 2022. Association of dhurrin levels and post-flowering non-senescence with resistance to stalk rot pathogens in sorghum bicolor. European Journal of Plant Pathology. 163:237-254. https://doi.org/10.1007/s10658-022-02473-2.
DOI: https://doi.org/10.1007/s10658-022-02473-2

Interpretive Summary: Sorghum is a drought-tolerant crop with multiple uses including for feed, food and biofuels. In spite of its drought tolerance, sorghum is vulnerable to the stalk rot diseases, Fusarium stalk rot and charcoal rot, especially during water stress. Stay-green lines maintain green leaves after flowering; i. e. the leaves do not senesce and dry-up as quickly. Stay-green lines tend to have greater resilience to drought and stalk rot diseases. However, the leaves and stalks also tend to have higher levels of a cyanide-producing compound, called dhurrin, that is toxic to animals. Our goal in this study was to identify Stay-green lines with increased resistance to stalk rots but lower dhurrin levels. By performing inoculations in the greenhouse, we identified four lines with increased resistance to the two stalk rot diseases: Plant Introduction (PI) 267379, PI 533882, PI 534053 and PI 534133. These four lines also exhibited increased resistance to Fusarium stalk rot in a field trial. We assessed the dhurrin levels of leaves from greenhouse-grown plants and found that PI 267379 and a senescent (non-Stay-green) disease-susceptible check, BTx623, had significantly less dhurrin than the Stay-green, high dhurrin, disease-resistant check, BTx642. When leaves from lines grown in the field were assessed, PI 267379 and PI 533882, as well as BTx623, had significantly lower dhurrin levels than BTx642. Field-grown lines were also scored at flowering for senescence using a 1 (Stay-green) to 5 (completely senescent) rating system. The PI 533882 and PI 534133 had senescence ratings similar to or even lower than that of BTx642 while PI 267379 and PI 534053 had higher ratings. Among lines exhibiting increased resistance, PI 267379 and PI 533882 show promise for breeding lines with increased stalk rot resistance, lower dhurrin levels and the Stay-green trait.

Technical Abstract: 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.