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Evolution of HPPD-Inhibitor Herbicide Resistance in a Waterhemp (Amaranthus tuberculatus var. rudis) Population from Nebraska, USA
The rapid adaptation of Amaranthus tubercultus (var. rudis) to modern agriculture made the species an excellent model for studying herbicide resistance evolution. Failure to control an A. tuberculatus (RW) population with postemergence (POST)-applied 4-hydroxyphenyl pyruvate dioxygenase (HPPD)-inhibitors was reported in northeast Nebraska, USA. The resistance was confirmed to mesotrione, tembotrione, and topramezone with dose-response studies. The RW population evolved a 2 to 18× resistance depending on the HPPD-inhibitor resistance herbicide being used. Nonetheless, premixes and tankmixes of multiple herbicide site-of-action (SOA) based on preemergence (PRE) only, POST only, and PRE followed by POST programs provided RW effective control (> 90%) under field conditions. The mechanism of resistance in the RW population is enhanced herbicide metabolism via P450 enzymes. The use of cytochrome P450 inhibitors (malathion, amitrole, and piperonyl butoxide) applied prior tembotrione, and topramezone reversed the RW phenotype to a susceptible phenotype; while amitrole only partially reversed mesotrione resistance. The use of cytochrome P450 inhibitors has a potential for combating metabolism-based resistance in RW population. However, the substrate specificity of P450 enzymes with HPPD- inhibitors highlighted the complexity of resistance in RW population. The genetic study showed that there is no dominance neither recessivity in mesotrione resistance inheritance in A. tuberculatus . In addition, mesotrione resistance is nuclear inherited and controlled by multiple genes. These results show that mesotrione resistance evolved slowly fostered by minor genes. These mesotrione resistance genes can be transferred under field conditions from RW to mesotrione susceptible A. palmeri (SP) and A. tuberculatus (SW) population. The gene flow study showed that interspecific (SP × RW) occurred at low frequencies and intraspecific (SW × RW) hybridization rapidly decrease with distance from the pollen-source. This result showed that pollen-mediated gene flow (PMGF) carrying metabolism-based resistance alleles occurs in weedy Amaranthus species. This result is significant as A. palmeri and A. tuberculatus are prolific seed producer and obligate outcrosser species. Therefore, even at low frequencies, PMGF can have important evolutionary consequences in weedy Amaranthus species.^
Coura Oliveira, Maxwel, "Evolution of HPPD-Inhibitor Herbicide Resistance in a Waterhemp (Amaranthus tuberculatus var. rudis) Population from Nebraska, USA" (2017). ETD collection for University of Nebraska - Lincoln. AAI10642740.