Distribution of resistant Aegilops tauschii populations across China and its target-site resistance mechanism.

Aegilops tauschii is a notorious weed that poses a severe threat to wheat production. Recently, its resistance to mesosulfuron-methyl has been increasingly documented in some provinces of China. With Ae. tauschii rapidly expanding its distribution range throughout China, however, its nationwide resistance distribution and the underlying resistance molecular mechanisms remain poorly understood. To address this knowledge gap, 305 populations of Ae. tauschii were collected from eight major wheat-growing provinces of China to characterize their nationwide resistance profiles and target-site resistance mechanisms. Of the populations examined, 83 populations from Shanxi, Shaanxi, Henan, Hebei, Shandong, and Jiangsu provinces exhibited varying levels of resistance to mesosulfuron-methyl. Resistant populations were particularly widespread in Shanxi and Shaanxi compared with other regions. Forty-seven resistant populations were then selected for target-site mutation analysis. A Pro-197-Leu substitution in the acetolactate synthase (ALS) gene was identified in 14 resistant populations, whereas no known resistance-conferring amino acid alteration was detected in the remaining 33 populations. Resistant populations carrying the Pro-197-Leu mutation displayed a higher resistance level than resistant populations without ALS gene mutations. Furthermore, in vitro ALS activity assays showed that populations with the Pro-197-Leu substitution were highly resistant to mesosulfuron-methyl, with resistance index (RI) ranging from 32.95 to 33.12. In contrast, the RI values of resistant populations lacking target-site mutations were below 2.90. To the best of our knowledge, this study represents the first report of a target-site mutation (Pro-197-Leu) conferring resistance to mesosulfuron-methyl in Ae. tauschii.