Enhanced CYP-450 herbicide metabolism and ALS Pro-197-Gln mutation endow different resistance levels to sulfonylureas herbicides in Lolium rigidum

VILA AIUB, MM; PONCE, DANIELA

Congreso; Global Herbicide Resistance Challenge 2017; 2017

Due to the allogamous nature of Lolium rigidum, multiple herbicide resistance is oftenobserved at the population and individual level. In the VLR69 L. rigidum population bothenhanced CYP-450 herbicide metabolism and target site ALS gene mutation (Pro-197-Gln) coexist at the individual level and endow resistance to ALS inhibiting herbicides. Itis unknown if incremental protection of plants from damage to a similar herbicide isprovided from stacked resistance genes. An experiment was conducted to estimate thedifferential survival to increasing chlorsulfuron and triasulfuron rates of L. rigidum plantsexhibiting only enhanced CYP-450 metabolism or both CYP-450 herbicide metabolismplus the specific homozygous (RR) ALS Pro-197-Gln mutation. Segregating herbicidesusceptible plants (WT) from within the origina,l field collected, VLR69 population(which contained both the CYP-450 metabolism and ALS mutation) were also used ascontrol. Wild-type plants showed a remarkable sensitivity for both herbicides and weretotally controlled even when exposed to the lowest chlorsulfuron (10 g/ha) andtriasulfuron (4 g/ha) dose. LD50 estimates associated with plants only expressingenhanced CYP-450 metabolism were 80 g/ha and 100 g/ha for chlorsulfuron andtriasulfuron, respectively. However, LD50 estimates associated with plants expressingboth the CYP-450 metabolism and specific ALS mutation were equal to (or higher than)2,560 g/ha and 1,024 g/ha for chlorsulfuron and triasulfuron, respectively. No mortalitywas observed in multiple resistant plants when even exposed to the highestchlorsulfuron (2,560 g/ha) and triasulfuron (1,024 g/ha) dose. At the normal field ratesCYP-450 metabolism endowed 95% and 75% survival to chlorsulfuron (20 g/ha) andtriasulfuron (32 g/ha), respectively. Overall, plants with only enhanced CYP-450metabolism showed an intermediate survival rate when compared to plants expressingboth CYP-450 metabolism plus the ALS Pro-197-Gln mutation under increasingherbicide rates. Further experiments are required to determine whether both enhancedCYP-450 ALS metabolism and ALS target site Pro-197-Gln mutation combine in aneutral, additive or multiplicative way to endow resistance to ALS inhibiting herbicides inL. rigidum.