ACCase and ALS susceptibility status of Echinochloa spp. populations in Anhui Province, China, and their baseline sensitivity to the HPPD inhibitor tembotrione

Echinochloa spp.are considered highly detrimental weeds, representing a substantial threat to rice (Oryza sativa L.) and maize (Zea mays L.) production in Anhui Province, China.Tembotrione, a 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide, was newly registered in China in 2021 for managing annual weeds in maize fields.This study aims to assess the susceptibility and extent of resistance in 85 Echinochloa spp.populations, collected from diverse rice and maize fields in Anhui Province, to two frequently employed herbicides: The acetyl-CoA carboxylase (ACCase) inhibitor metamifop and the acetolactate synthetase (ALS) inhibitor penoxsulam.The study also seeks to determine their baseline sensitivity to tembotrione, and evaluate the potential risk of herbicide resistance development in these populations.Single-dose testing confirmed that among the 85 populations, 44 were resistant to metamifop, with resistance index (RI) ranging from 2.07 to 10.80; 63 were resistant to penoxsulam, with RI ranging from 2.06 to 16.04; 30 were resistant to both metamifop and penoxsulam.Target gene sequencing revealed a common Trp-574-Leu mutation in five penoxsulam-resistant populations.Subsequently, whole plant dose-response showed that the tembotrione doses causing 50% growth reduction (GR50 values) in the 85 populations ranged from 6.34 to 43.94 g ai ha -1 .Meanwhile, the frequency of the GR50 values was not normally distributed but distributed as a unimodal curve and extending towards the sensitive end.The baseline sensitivity (GR50b) to tembotrione was 17.96 g ai ha -1 and the baseline sensitivity index (SI50) was 6.93.