Inheritance of Triazine Resistance in Poa Annua: Consequences for Population Dynamics

S ummary A chloroplast triazine resistant population of Poa annua from a triazine treated area was compared with one from an adjacent untreated area. A study of morphological characters and isoenzymes showed that the resistant population contained as much polymorphism as the susceptible one. One phenotype, on an isozyme basis, was much more frequent in each habitat, suggesting the importance of natural selection in each population. The possibility of a ‘founder effect’ within the resistant population is discussed. A dominant esterase allozyme was used to estimate the outcrossing rate giving an estimate of 13 % under greenhouse conditions. Transmission of herbicide resistance was also tested and found to be mainly inherited maternally (0·1% transmission via pollen). Paternal transmission is therefore not important for gene flow. Allogamy would appear responsible for the high degree of polymorphism found in the resistant population.