Response of sorghum lines carrying recently identified brown midrib (bmr) mutations to stalk rot pathogens and water deficit

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

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2023
Publication Date: 4/7/2023
Citation: Funnell-Harris, D.L., Sattler, S.E., Toy, J.J., Oneill, P.M., Bernhardson, L.F. 2023. Response of sorghum lines carrying recently identified brown midrib (bmr) mutations to stalk rot pathogens and water deficit. Plant Pathology. https://doi.org/10.1111/ppa.13702.
DOI: https://doi.org/10.1111/ppa.13702

Interpretive Summary: The stalk diseases Fusarium stalk rot and charcoal rot cause significant losses of sorghum biomass in the U.S. These diseases can result in plant lodging, which impedes biomass and grain harvest. These diseases are particularly insidious when water is limited, especially under drought conditions during flowering. ARS scientists at Lincoln, NE screened brown midrib (bmr) mutant lines with reduced lignin levels, the component of stalk tissue that reduces livestock digestibility and conversion efficiency of lignocellulosic feedstock to bioenergy products. Six new bmr mutant lines were developed with reduced lignin levels in three different sorghum varieties. These sorghums were screened for responses to three stalk pathogens. The bmr29-1 or bmr31-1 lines may be promising for developing sorghum with altered lignin and resistance to stalk pathogens. These lines were further tested using a method developed to evaluate sorghum under drought conditions in a greenhouse. One variety commonly used for hybrid seed development was highly susceptible to charcoal rot under drought conditions, but the bmr29-1 or bmr31-1 lines were as resistant to these conditions as when adequately watered. All the other lines tested were as resistant to the pathogens as normal sorghums. These results showed that bmr29-1 and bmr31-1 can be used to develop cultivars and hybrids with resilience to drought and stalk pathogens, while reducing lignin for forage and bioenergy feedstock improvement.

Technical Abstract: Sorghum [Sorghum bicolor (L.) Moench] is drought-tolerant and has diverse germplasm for food, feed, forage and bioenergy. However, stalk diseases reduce quality and yield of biomass and grain, especially under drought. Previously, brown midrib (bmr) mutations in monolignol biosynthesis were shown to reduce lignin content and alter composition, but were not more susceptible to stalk diseases than wild-type lines. Recently-characterized bmr mutations were shown to affect flavonoid biosynthesis (chalcone isomerase; bmr30-1) or 1-carbon metabolism (folylpolyglutamate synthase; bmr19-1107, bmr19-1168 and bmr19-1937). Two other mutations, bmr29-1 and bmr31-1, have not yet been characterized. The six mutations were incorporated into elite genetic backgrounds (RTx430, BTx623 and BWheatland) to develop near-isogenic lines containing each mutation. Using peduncle inoculations with Fusarium thapsinum and F. proliferatum (Fusarium stalk rot) and Macrophomina phaseolina (charcoal rot) under well-watered conditions, most bmr lines were at least as resistant as corresponding wild-type, except for RTx430 bmr19-1937 that had significantly longer mean lesion lengths when inoculated with M. phaseolina. Based on significantly reduced lesion lengths following inoculations with F. proliferatum and F. thapsinum, respectively, bmr29-1 and bmr31-1 lines were screened using basal stalk inoculations under well-watered and water-deficit conditions. The bmr lines were at least as resistant as corresponding wild-type lines. Wild-type BTx623 was highly susceptible to M. phaseolina under water-deficit, but near-isogenic bmr29-1 and bmr31-1 lines had significantly shorter mean lesion lengths. Incorporation of these mutations can increase resistance to stalk pathogens in cultivar and hybrid development for feed, bioenergy and production of biomass-based green chemicals.