Evolution of Herbicide Resistance in Senecio vulgaris: Variation in Susceptibility to Simazine Between and Within Populations

SUMMARY (1) Inter-population variation in susceptibility to simazine in Senecio vulgaris was investigated in forty-six different populations collected from several different fruit farming locations in England. Significant population differences occurred in susceptibility to simazine indicating a genetic basis for variation in susceptibility. (2) There was a positive, linear relationship between percentage survival of a population and the number of consecutive years of simazine application indicating the possibility that natural selection had occurred. (3) Intra-population variation in susceptibility to simazine was investigated in one population originating from an apple orchard in Suffolk and a selfing series procedure was used to obtain the genetic and environmental components of variance and an estimate of broad sense heritability. The latter was low.