ELECTROPHORETIC VARIATION IN TRIAZINE-RESISTANT AND SUSCEPTIBLE POPULATIONS OF AMARANTHUS RETROFLEXUS L

Patterns of electrophoretic variation in seven enzyme systems were investigated in one triazine-resistant and nine susceptible populations of Amaranthus retraflexus L. collected along an 800 km north-south transect in southern Ontario, Canada. The resistant population occurs in a field in which continuous maize production and intensive use of atrazine had been combined over a 15-year period. The nine susceptible populations were collected from both waste ground and cultivated fields. One would expect the genetic make-up of the triazine-resistant population to be simpler than that of susceptible populations as a result of founder effects from a single or only a few resistant founder plants. Our results confirmed this prediction. The resistant population showed a marked reduction in genetic variation, as compared with susceptible populations. One enzyme, GDH, was monomorphic in all 10 populations, the other six enzymes (IDH, GOT, 6PGD, PGI, LAP and MDH) showed varying degrees of phenotypic polymorphism. The resistant population was variable for three of the seven enzyme systems examined. This was in contrast to the homogeneity observed in triazine-resistant populations of Chenopodium album L. from Ontario. Differences in within-population phenotypic polymorphism among the nine susceptible populations of A. rctroflexus were not correlated with habitat or latitude of collection sites.