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Postemergence grass weed control continues to be a major challenge in grain sorghum [Sorghum bicolor (L.) Moench], primarily due to lack of herbicide options registered for use in this crop. The development of herbicide-resistant sorghum technology to facilitate broad-spectrum postemergence weed control can be an economical and viable solution. The 4-hydroxyphenylpyruvate dioxygenase-inhibitor herbicides (e.g., mesotrione or tembotrione) can control a broad spectrum of weeds including grasses, which, however, are not registered for postemergence application in sorghum due to crop injury. In this study, we identified two tembotrione-resistant sorghum genotypes (G-200, G-350) and one susceptible genotype (S-1) by screening 317 sorghum lines from a sorghum association panel (SAP). These tembotrione-resistant and tembotrione-susceptible genotypes were evaluated in a tembotrione dose–response [0, 5.75, 11.5, 23, 46, 92 (label recommended dose), 184, 368, and 736 g ai ha–1] assay. Compared with S-1, the genotypes G-200 and G-350 exhibited 10- and seven fold more resistance to tembotrione, respectively. To understand the inheritance of tembotrione-resistant trait, crosses were performed using S-1 and G-200 or G-350 to generate F1 and F2 progeny. The F1 and F2 progeny were assessed for their response to tembotrione treatment. Genetic analyses of the F1 and F2 progeny demonstrated that the tembotrione resistance in G-200 and G-350 is a partially dominant polygenic trait. Furthermore, cytochrome P450 (CYP)-inhibitor assay using malathion and piperonyl butoxide suggested possible CYP-mediated metabolism of tembotrione in G-200 and G-350. Genotype-by-sequencing based quantitative trait loci (QTL) mapping revealed QTLs associated with tembotrione resistance in G-200 and G-350 genotypes. Overall, the genotypes G-200 and G-350 confer a high level of metabolic resistance to tembotrione and controlled by a polygenic trait. There is an enormous potential to introgress the tembotrione resistance into breeding lines to develop agronomically desirable sorghum hybrids.

Mesotrione is effective in controlling a wide spectrum of weeds in corn but not registered for postemergence use in sorghum because of crop injury. We screened a sorghum germplasm collection and identified two mesotrione-resistant sorghum genotypes (G-1 and G-10) and one susceptible genotype (S-1) in an in vitro plate assay. A mesotrione dose−response assay under greenhouse and field conditions confirmed that G-1 and G-10 are highly resistant compared to S-1. We found enhanced metabolism of mesotrione in G-1 and G-10 using HPLC assay, and a significant reduction in biomass accumulation was found in G-1 and G-10 plants pretreated with cytochrome P450 (CYP)-inhibitors malathion or piperonyl butoxide, indicating the involvement of CYPs in the metabolism of mesotrione. Genetic analyses using F 1 and F 2 progenies generated by crossing G-1 and G-10 separately with S-1 revealed that mesotrione resistance in sorghum is controlled by a single dominant gene along with several genes with minor effects.

Muscadine grapes (Vitis rotundifolia Michx.) are a specialty crop cultivated in the southern United States. Muscadines (2n=40) belong to the Muscadinia subgenus of Vitis, while all other cultivated grape species belong to the subgenus Euvitis (2n=38). The berry color locus in muscadines has been mapped to a 0.8 Mbp region syntenic with chromosome 4 of V. vinifera. In this study, we identified glutathione S-transferase4 (GST4) as a likely candidate gene for anthocyanin transport within the berry color locus. PCR and KASP genotyping identified a single intragenic SNP (C/T) marker corresponding to a proline to leucine mutation within the muscadine GST4 (VrGST4) that differentiated black (CC and CT) from bronze (TT) muscadines in 65 breeding selections, 14 cultivars, and 320 progeny from two mapping populations. Anthocyanin profiling on a subset of the progeny indicated a dominant VrGST4 action, with no allele dosage effect on total anthocyanin content or composition of individual anthocyanins. Proanthocyanidin content was similar in the seeds of both black and bronze genotypes, and seeds had much higher VrGST3 expression and lower VrGST4 expression than skins. VrGST4 expression was higher in post-veraison berries of black muscadines compared to pre-veraison berries, but no changes in gene expression in pre- and post-veraison berries were observed in the bronze muscadine cultivar. VrMybA1 expression was higher in post-veraison berries of both black and bronze muscadines. These results suggest that berry pigmentation in muscadines is regulated by a mechanism distinct from the MybA gene cluster that is responsible for berry color variation in V. vinifera.

Muscadine grapes (Vitis rotundifolia Michx.) are a specialty crop cultivated in the southern United States. Muscadines (2n = 40) belong to the Muscadinia subgenus of Vitis, while other cultivated grape species belong to the subgenus Euvitis (2n = 38). The muscadine berry color locus was mapped to a 0.8 Mbp region syntenic with chromosome 4 of V. vinifera. In this study, we identified glutathione S-transferase4 (GST4) as a likely candidate gene for anthocyanin transport within the berry color locus. PCR and KASP genotyping identified a single intragenic SNP (C/T) marker corresponding to a proline to leucine mutation within the muscadine GST4 (VrGST4) that differentiated black (CC and CT) from bronze (TT) muscadines in 126 breeding selections, 76 cultivars, and 359 progeny from three mapping populations. Anthocyanin profiling on a subset of the progeny indicated a dominant VrGST4 action. VrGST4 was expressed in skins of both black and bronze muscadines at similar levels. While non-synonymous polymorphisms between black and bronze muscadines were discovered in VrGSTF12, another Type I GST-coding gene in the muscadine color locus, this gene was ruled out as a possible candidate for berry color because RNA sequencing indicated it is not expressed in berry skins at véraison from black or bronze genotypes. These results suggest that the bronze phenotype in muscadines is regulated by a mechanism distinct from the MybA gene cluster responsible for berry color variation in V. vinifera.

Plant growth stage and temperature influence the activity of glyphosate on common lambsquarters. A biotype of common lambsquarters in Dickinson County, KS (DK) was not controlled upon treatment with glyphosate in the field. In a greenhouse dose–response study, the DK biotype expressed 1.5-fold less sensitivity to glyphosate compared to a known susceptible biotype from Riley County, KS (RL). Common lambsquarters plants were treated at different growth stages (5 to 7, 10 to 12, 15 to 17, or 19 to 21 cm tall) with glyphosate at a field rate (840 g ae ha–1), and, regardless of the biotype, plants were more susceptible to glyphosate when they were 5 to 7 cm tall. Common lambsquarters plants were treated with glyphosate (840 g ae ha–1) after growing at different temperatures (25/15, 32.5/22.5, or 40/30 C day/night), and regardless of the biotype, plants were more susceptible to glyphosate when grown at 25/15 C. The results suggest that the DK biotype exhibits reduced sensitivity to glyphosate compared to the RL biotype, and glyphosate applied at field rate would be more effective on smaller common lambsquarters plants and at cooler temperatures. Common lambsquarters seedlings tend to emerge when temperatures are cooler, early in the spring relative to other summer annual weeds. Therefore, plants should be identified and treated earlier in the growing season for best efficacy with glyphosate.

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