Quantifying the level of seed germiabiliy of herbicide-resistant (R) and susceptible (S) weeds is useful for understanding theevolutionary development of herbicide resistance, but also for implementing herbicide-resistance management strategies.Germination is a crucial aspect in the life phase of weeds. Phalaris brachystachys biotypes resistant to ACCase-inhibitingherbicides have been confirmed in wheat fields in Iran. This study aimed to investigate the germination behaviour of ACCase-resistant and susceptible subpopulations P. brachystachys under different environmental factors. An analysis of the seedgermination of P. brachystachys sub populations at the seed stage was therefore conducted. The resistant (R) and susceptible(S) P. brachystachys subpopulation germination traits were tested in different temperature, salinity stress, drought, and burialdepth conditions. All tests were carried out with five replications in a completely randomized design. The highest germina-tion percentage in both subpopulations occurred at a temperature range of 20 to 25 °C. At 35 °C, no germination occurred.In terms of estimated cardinal temperatures, no differences were observed between S and R subpopulations. Seeds contain-ing the ACCase Ile-1781-Thr mutation germinated better under salt and osmotic stress. There were no fitness differences inpH conditions. The percentage and rate of emergence of the R subpopulation were more than S subpopulation at differentburial depths. The seedling emergence reached a maximum of 50% in the S subpopulation at a depth of 6.65 cm and in the Rsubpopulation at depths of 9.81 cm, respectively. Significant differences in seed germination were found between herbicide-resistant and susceptible sub population, and the pleiotropic effect of resistant alleles on germination and seed emergenceunder different environmental conditions was demonstrated. Results suggested that deep tillage operations and the delayedsowing of autumn-sown crops could control resistant populations that emerge more rapidly than S population; therefore, theprevalence in the R population may decrease.

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