Genetic diversity and population structure of ALS-resistant Amaranthus hybridus across Brazil's primary soybean-growing regions

BACKGROUND: Resistance to acetolactate synthase (ALS)-inhibiting herbicides has emerged in Amaranthus hybridus populations across Brazil's soybean-growing regions. To gain insights into the evolutionary origins and spread of resistance, this study (1) investigated the ALS inhibitor resistance mechanisms in nine A. hybridus populations and (2) assessed their genetic diversity, structure, and relatedness. RESULTS: Resistance to the ALS inhibitor chlorimuron in A. hybridus was associated with two distinct target-site mutations: Trp-574-Leu and Asp-376-Glu. Population genetics revealed low levels of genetic diversity (H_E = 0.00117 to 0.16019; π = 0.00126 to 0.17421) and inbreeding (F_IS = 0.0015 to 0.13157). Principal component analysis differentiated A. hybridus by geographical region, while ADMIXTURE analysis revealed population structure with evidence of admixture between genetic clusters in three groups of populations. CONCLUSION: The results suggest multiple local and independent evolutionary origins of resistance. The spread of resistance is primarily driven by local herbicide selection pressure and gene flow through seed dispersal.