Intraspecific variability of the acetolactate synthase gene

Abstract

Common ragweed and common cocklebur plants were collected at two sites each in Illinois, Minnesota, and Ohio to analyze intraspecific variability of the gene encoding acetolactate synthase (ALS). A 385-nucleotide fragment within the coding sequence ofALSwas compared among 24 plants of each of these two species from the six locations. Common ragweedALSwas highly variable, with polymorphisms observed at 48 (12.5%) of the 385 nucleotides among the 24 plants. Despite the numerous nucleotide polymorphisms, only two inferred amino acid polymorphisms were identified. No apparent population structure was suggested by theALSsequence data, indicating widespread gene flow consistent with the wind-pollinated nature of common ragweed. In contrast to common ragweed, noALSpolymorphisms were identified among the common cocklebur plants used in this study. As a basis for comparing the extremes observed between common ragweed and common cocklebur,ALSintraspecific variability also was investigated in 10 plants each of tall waterhemp and smooth pigweed. Normalized to the number of plants analyzed, the number of nucleotide polymorphisms for both tall waterhemp and smooth pigweed was greater than that in common cocklebur but less than that observed in common ragweed. Information on variability of herbicide target-site genes may be useful in predicting the likelihood for herbicide-resistance development. However, all four of the species investigated in this study have evolved resistance to ALS-inhibiting herbicides, despite the different levels ofALSvariability observed.