Lactofen tolerance in commercial chickpea (Cicer arietinum l.) genotypes: the role of herbicide metabolism

Background: Chickpeas ( Cicer arietinum) ) are an important type of pulse whose production is hindered by poor weed control. Objective: To assess lactofen selectivity levels and to uncover tolerance mechanisms in commercial genotypes. Methods: Four genotypes and weed species were grown under controlled-environment conditions and subjected to lactofen dose-response assays (11.2-2,880 g a.i. ha-1 ). Visual evaluations performed until 35 days after application, when biomass was quantified and selectivity indexes obtained using regression analysis. Following 14 C-lactofen application, absorption and translocation were assessed until 168h after treatment (HAT), when chickpea plants were washed to remove the unabsorbed herbicide or subjected to autoradiography and tissue combustion. Lastly, 14 C-lactofen was applied and metabolites extracted at 96 HAT, and their retention factors (Rf) determined by thin layer chromatography and radioscanner reading. Results: Tridax procumbens and Amaranthus spinosus were highly susceptible to lactofen. Chickpea genotypes tolerated lactofen at the highest labelled used rate in soybeans (180 g a.i. ha-1 ). Lactofen absorption was high (88.1%-94.6%) and translocation was limited (< 2.5%) across genotypes- a similar trend observed in susceptible species, and hence are not implicated in lactofen tolerance. One main metabolite was found in chickpea genotypes, accounting for 12.5%-19.4% of applied radioactivity; the chickpea genotype with the highest tolerance level (BRS Cicero) was the only one in which two metabolites were quantified. Altogether, these results suggest that lactofen tolerance in chickpeas could be conferred by enhanced herbicide metabolism. Conclusions: Lactofen could become an option for selective, post-emergence weed control in chickpeas.