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

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Abstract
Patterns of electrophoretic variation in seven enzyme systems were investigated in one triazine-resistant and nine susceptible populations of Amaranthus retroflexus 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 [glutamate dehydrogenase], was monomorphic in all 10 populations, the other six enzymes (IDH [isocitrate dehydrosenase], GOT [aspartate aminotransferase], 6PGD [6-phosphogluconate dehydrogenase], PGI [phosphoglucose isomerase], LAP [leucine aminopeptidase] and MDH [malate dehydrogenase]) 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. retroflexus were not correlated with habitat or latitude of collection sites.