Different cross-resistance patterns to AHAS herbicides of two tribenuron-methyl resistant flixweed (Descurainiasophia L.) biotypes in China.

Flixweed (Descurainiasophia L.) is a troublesome weed in winter wheat fields in China. Two flixweed accessions, HB08 and HB16 with a Pro-197-Leu and Pro-197-Ser AHAS-mutation respectively, have evolved very high levels resistance to sulfonylurea (SU) herbicide, tribenuron-methyl. Cross resistance of HB08 and HB16 to AHAS herbicides of SU, imidazolinone (IMI), triazolopyrimidine (TP) and pyrimidinyl-thiobenozoate (PTB) families was investigated by dose-response experiments. In addition, the effects of AHAS herbicides on the activity of AHAS extracted from HB08 and HB16 plants were evaluated. HB16 exhibited cross resistance to SU herbicides halosulfuron-methyl and triasulfuron, TP herbicides flumetsulam and penoxsulam, but displayed more sensitivity to IMI herbicide imazethapyr. By contrast, HB08 only showed cross resistance to SU herbicides halosulfuron-methyl and triasulfuron. The in vitro sensitivity of AHAS to AHAS herbicides is consistent with the results of dose-response experiments and the estimated Pearson's r values for HB08 and HB16 are 0.996 and 0.912 respectively. These indicated that altered AHAS sensitivity was responsible mainly for cross resistance patterns observed in the two resistant biotypes.