Abstract
Herbicide application is crucial for weed management in most crop production systems, but for sorghum herbicide options are limited. Sorghum is sensitive to residual protoporphyrinogen oxidase (PPO)-inhibiting herbicides, such as fomesafen, and a long re-entry period is required before sorghum can be planted after its application. Improving sorghum for tolerance to such residual herbicides would allow for increased sorghum production and the expansion of herbicide options for growers. In this study, we observed sorghum tolerance to residual fomesafen. To investigate the underlying tolerance mechanism a genome-wide association mapping study was conducted using field-collected sorghum biomass panel (SBP) data, and a greenhouse assay was developed to confirm the field phenotypes. A total of 26 significant SNPs (FDR<0.05), spanning a 215.3 kb region on chromosome 3, were detected. The ten most significant SNPs included two in genic regions (Sobic.003G136800, and Sobic.003G136900) and eight SNPs in the intergenic region encompassing the genes Sobic.003G136700, Sobic.003G136800, Sobic.003G137000, Sobic.003G136900, and Sobic.003G137100. The gene Sobic.003G137100 (PPXI), which encodes the PPO1 enzyme, one of the targets of PPO-inhibiting herbicides, was located 12kb downstream of the significant SNP S03_13152838. We found that PPXI is highly conserved in sorghum and expression does not significantly differ between tolerant and sensitive sorghum lines. Our results suggest that PPXI most likely does not underlie the observed herbicide tolerance. Instead, the mechanism underlying herbicide tolerance in the SBP is likely metabolism-based resistance, possibly regulated by the action of multiple genes. Further research is necessary to confirm candidate genes and their functions.
Highlights
Weed infestation is a major crop production constraint
Herbicide resistance mechanisms can be classified into two categories: target site resistance (TSR) and non-target site resistance (NTSR)
Metabolism-based NTSR is associated with the herbicide detoxification due to the increased activity of enzyme complexes, including esterases, cytochrome P450s, glutathione S-transferase (GSTs), and UDP-glucosyl transferase [32]
Summary
Weed infestation is a major crop production constraint. Herbicide application is a critical control strategy in most crop production systems, and modern agriculture relies heavily on herbicides for weed suppression. A limited number of herbicides are available for sorghum, and the herbicide options for grass control are even lower [1]. Sorghum is sensitive to many commonly used herbicides and is sometimes injured by herbicides labeled.
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