Resistance to acetolactate synthase-inhibiting herbicides in Capsella bursa-pastoris and its molecular resistance mechanism

Whole-plant dose-response experiments were conducted to investigate the resistance levels to tribenuron-methyl and other five kinds of acetolactate synthase (ALS)-inhibiting herbicides of Capsella bursa-pastoris population. To identify its molecular resistance mechanism, ALS gene fragments were amplified, sequenced and compared with the susceptible population. The results showed that the resistant population 15-ZMD-5 had evolved high-level resistance to tribenuron-methyl compared with the susceptible population 15-ZMD-1, and the resistance index was 219.6. There were three different kinds of mutation at ALS sequence in the resistant population:CCT (Pro)-197-CTT (Leu), TGG (Trp)-574-TTG (Leu), and all of the mutations occur at the same time. The tribenuron-methyl-resistant 15-ZMD-5 population showed high-level cross-resistance to pyrithiobac sodium, pyroxsulam and flucarbazone-Na, with resistance index of 41.2, 79.3 and 87.8, respectively, and low-level crossresistance to florasulam and imazethapyr with resistance index of 8.5 and 5.6, respectively. This study demonstrated that the mutation in the ALS gene was one of main reasons for the resistance to LSinhibiting herbicides in shepherd's purse populations.