Geographical variation in populations of Chenopodium album resistant and susceptible to atrazine. I. Between- and within-population variation in growth and response to atrazine

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Abstract
Between-and within-population variation in growth characteristics, isoenzyme patterns and response to atrazine were studied in individuals from 4 atrazine-resistant (R) and 4 susceptible (S) populations of C. album L. collected from sites of contrasting climate in southern Ontario [Canada]. In both the R and S types, population differences in growth characteristcs were correlated with geographical location and climatic differences. The more northerly R and S populations had a greater rate of development, earlier maturation, lower biomass at maturity, and greater reproductive effort compared, respectively, with the more southerly R and S populations. Estimates of within-population variation were obtained statistically for a number of growth characters and from the electrophoretic patterns of 5 enzyme systems. These indicated marked homogeneity in the 4 R populations as compared with the more variable S populations. Populations from the 2 disjunct areas of resistance were different for 2 of the enzymes studied and would appear to represent 2 different genotypes. Mutation for resistance in populations of C. album has apparently occurred independently in the 2 areas. Coupled with the evidence for differential growth characteristics of these 2 genotypes in response to climate, resistance has apparently developed in individuals already established in each of the 2 separate areas, rather than spreading from a single recent introduction of the R type in Ontario. As expected, distinct differences between the R and S types were obtained in response to postemergence treatments with atrazine. The 4 R populations either showed no effect or exhibited increased growth. S populations all showed marked decreases in growth and production of biomass. Significant between-population differences in growth features were apparent for both types in the control and were maintained in the presence of atrazine. Although small differences in relative susceptibility were obtained for the susceptible populations, statistically significant population by treatment interactions were not evident.