Evolution of resistance to HPPD‐inhibiting herbicides in a wild radish population via enhanced herbicide metabolism.

BACKGROUND: Relatively new herbicides that target 4‐hydroxyphenylpyruvate dioxygenase (HPPD) are now available for use on the world's great grain crops (rice, wheat, corn and soybean) and for other uses. With widespread and persistent use of HPPD‐inhibiting herbicides, the evolution of HPPD‐inhibiting herbicide resistant weeds is inevitable. Currently, resistance to HPPD‐inhibiting herbicides is known in two weed species, waterhemp and Palmer amaranth. Here, we report a HPPD‐inhibiting herbicide resistant wild radish population from the Western Australia grain belt. This population was not selected with HPPD‐inhibiting herbicides, rather it evolved resistance to earlier used herbicides with different modes of action and exhibits cross‐resistance to HPPD‐inhibiting herbicides. RESULTS: Dose–response experiments showed the resistant (R) population exhibits 4 to 6.5‐fold resistance to the HPPD‐inhibiting herbicides mesotrione, tembotrione and isoxaflutole, compared to the susceptible (S) population. This resistance is not target‐site based as cloning of full coding sequences of the HPPD genes from S and R plants did not reveal resistance‐endowing single nucleotide polymorphisms. The HPPD gene expression levels are similar in S and R plants. In addition, no differences in [14C]‐mesotrione uptake and translocation were observed in the S and R plants. However, the time required for R plants to metabolise 50% [14C]‐mesotrione is 7.7‐fold faster than for the S plants. CONCLUSION: We confirm resistance to HPPD‐inhibiting herbicides exists in a population of the economically damaging global weed wild radish. The resistance in this population is due to a non‐target‐site based enhanced rate of herbicide metabolism. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]