Interpreting the Evolution of a Triazine‐resistant Population of Poa Annua L.

SUMMARY The frequency of esterase isozyme genotypes was analysed both in a triazine‐resistant population and in susceptible populations. The main findings were (i) a low polymorphism, (ii) a high rate of heterozygotes at one particular locus; this polymorphism being related to the growth form, (iii) a higher proportion of prostrate plants then would usually be expected in an open habitat. This genetic structure could result from a recent founder event in a triazine‐treated area followed by an increase of polymorphism through gene migration from adjacent populations. The importance of environmental conditions (other than triazine treatments) on the evolution of populations is discussed.