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Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/10/2018 Publication Date: 9/3/2018 Publication URL: http://handle.nal.usda.gov/10113/6082924 Citation: Funnell-Harris, D.L., Oneill, P.M., Sattler, S.E. 2018. Field response of near-isogenic brown midrib sorghum lines to fusarium stalk rot, and response of wildtype lines to controlled water deficit. Plant Pathology. 67:1474-1482. https://doi.org/10.1111/ppa.12863. DOI: https://doi.org/10.1111/ppa.12863 Interpretive Summary: Fusarium stalk rot of sorghum is a destructive disease that under drought conditions reduces grain and biomass yields and can lead to lodging, making the crop unharvestable. Lines with the brown midrib trait (bmr), that have increased digestibility for livestock and usability for biomass bioenergy, have reduced lignin. Lines with two different genes (bmr6 and bmr12), and the genes stacked, were developed in two normal cultivar backgrounds. However, lignin is a compound that is considered important in preventing fungal infections, plant disease and lodging. The bmr and normal lines were infected with the Fusarium stalk rot pathogen at two field locations, one irrigated and the other dryland, in Nebraska. None of the bmr lines had more disease than their normal lines, following infection at both locations. However, the stacked line in one background seemed to be more resistant than the normal line in the same background when grown under irrigation. These results showed that the low lignin lines are usable for development of hybrids, for increased uses for animal feed and biomass bioenergy and can be grown under dryland conditions and withstand Fusarium stalk rot infections. A greenhouse experiment was also developed that infects plants with Fusarium stalk rot while under drought-like conditions. This will allow us to more quickly test lines for resistance to Fusarium stalk rot under drought conditions. Technical Abstract: To increase digestibility for ruminant livestock and for lignocellulosic ethanol conversion efficiency in sorghum (Sorghum bicolor), brown midrib (bmr) lines carrying bmr6 or bmr12 and the double mutant (bmr6 bmr12) in two backgrounds (RTx430 and Wheatland) were developed, resulting in lines with significantly reduced lignin, as compared with the nearisogenic wildtype. Under greenhouse conditions, these lines had previously demonstrated no increased susceptibility, and some lines were more resistant to the highly virulent stalk rot pathogen, Fusarium thapsinum, compared to the wildtype. Fusarium stalk rot of sorghum is a destructive disease that under high temperatures or drought conditions may lead to lodging. To determine if greenhouse observations could be extended to field environments, bmr and near-isogenic wildtype lines were inoculated with F. thapsinum at field locations, Mead (irrigated) and Havelock (dryland) in Nebraska, USA. Analysis of mean lesion lengths showed those of most bmr lines were statistically similar to the wildtype. Across both genetic backgrounds, bmr6 and bmr6 bmr12 double mutant plants grown at Mead had significantly smaller mean lesion lengths than the corresponding wildtype (P = 0.05). To assess responses of the two genetic backgrounds to controlled (greenhouse) water stress, wildtype RTx430 and Wheatland plants were inoculated with F. thapsinum under well-watered and water stress conditions. Mean lesion lengths resulting on water deficit plants were significantly larger than those on well-watered plants (P = 0.01). These results indicate that this bioassay can be used to screen sorghum lines in the greenhouse for increased resistance or tolerance to both drought and fusarium stalk rot. |
