Abstract

Italian ryegrass [Lolium perenne ssp. multiflorum (Lam.)] is a problematic C3 annual weed in winter wheat and other crops in the US, continental Europe. The objective of this research was to assess the expression profiles of herbicide target-site genes upon treatment with field rates of ALS- (e.g., chlorsulfuron), PSII- (e.g., atrazine), EPSPS- (e.g., glyphosate), and HPPD- (e.g., mesotrione) inhibitors, respectively in Italian ryegrass. Furthermore, the expression of the genes in chloroplasts that contribute to photosynthesis and CO₂ assimilation was also measured in response to these herbicide treatments. LmALS was upregulated (> 3-fold) whereas LmpsbA was downregulated (> 40-fold) at 8 h after chlorsulfuron and atrazine treatments respectively. However, LmEPSPS gene expression remained similar to control levels at 8 h after glyphosate treatment. LmHPPD gene showed > 1-fold higher expression at 8 h after mesotrione treatment. LmCAB, a major component of the photosystem II light-harvesting complex, was downregulated immediately (8 h) after chlorsulfuron, atrazine, glyphosate, and mesotrione treatments respectively. Similarly, LmRubisco, was downregulated after glyphosate and mesotrione treatments. However, LmRubisco was upregulated 0.4-fold after chlorsulfuron treatment and remained unaffected after atrazine treatment. Overall, the data from this study suggest that the treatment with herbicides showed variation in expression of herbicide target genes and those that are involved in the critical photosynthetic pathway.

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