Abstract
Echinochloa crus-galli is a grass weed that infests rice fields and causes significant crop yield losses. In this study, we surveyed 15 resistant E. crus-galli populations collected from rice fields in Hubei Province, China, and investigated the resistance levels and target site resistance mechanisms to the acetolactate synthase (ALS) inhibitor penoxsulam. The results of whole-plant bioassay experiments revealed that 15 populations presented different levels of resistance to penoxsulam. The Trp-574-Leu mutation was detected in ten resistant populations, and the Pro-197-Leu mutation was detected in one resistant population. Additionally, the in vitro ALS activity in resistant populations (18-ETF, 18-WJJ, and 18-WMJ) was 51.28-, 5.51-, and 8.46-fold greater than that in the susceptible population. The ALS from these resistant populations requires a much higher penoxsulam concentration for activity inhibition. ALS gene expression in three resistant populations (18-ETF, 18-WJJ, and 18-WMJ) was 1.53-, 1.58-, and 1.41-fold greater than that in the susceptible population 18-NJ before penoxsulam treatment. Our results indicated that target-site mutation in ALS is at least partially responsible for barnyardgrass resistance to penoxsulam in Hubei Province.