Sterile oat [Avena sterilis L. ssp. ludoviciana (Durieu) Gillet & Magne] is rapidly proliferating in cereal fields across northeastern and northwestern Iran, underscoring the necessity of studying its ecology in these two distinct climates. A study was conducted to assess the impact of environmental factors on the germination of two native populations of A. sterilis. The germination responses of populations from Mashhad (northeastern Iran) and Tabriz (northwestern Iran) were evaluated under various treatments, including temperature, osmotic potential, NaCl concentration, and light/dark cycles. As the temperature increased and osmotic potential decreased—indicating heightened drought stress—the germination percentages of both populations declined. The Mashhad population exhibited the highest germination percentages, reaching 99% at 10 C and 100% at 15 C, both under 0 MPa osmotic potential. Conversely, the Tabriz population demonstrated its peak germination percentages at 15 C and 20 C, also under 0 MPa osmotic potential, with rates of 97% and 96%, respectively. The highest germination rates were observed in seeds from the Mashhad and Tabriz populations at 15 C, with osmotic potentials of 0 MPa and −0.3 MPa, yielding rates of 0.52 and 0.48 seeds d−1, respectively. The NaCl concentration required for 50% inhibition of seed germination was 4.76 dS m−1 for the Mashhad population and 3.90 dS m−1 for the Tabriz population. In both populations, the highest germination percentage was observed under a light/dark cycle of 10 h of light and 14 h of darkness. The differences in germination responses between the Mashhad and Tabriz populations can be attributed to local environmental adaptations. Variations in temperature, osmotic potential, and other climatic factors influence seed dormancy and germination traits, enabling populations to thrive in their specific habitats. These local adaptations contribute to differences in germination performance under various environmental conditions, ultimately affecting their potential spread across different regions.

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