Germination response of turkish pine (Pinus brutia Ten.) seeds under low temperature stress

In this study, the effects of low temperature stress on germination were investigated in seeds of six different red pine (Pinus brutia Ten.) origins representing different altitude and bioclimatic zones. For this purpose, first, thousand-grain weight and humidity levels were determined in the seeds. Low temperature tests on seeds were carried out at 3 different humidity levels (air dry RH 10%, semi-saturated RH 20%, fully saturated RH 30%) and 6 different temperatures (control, -5, -10, -15, -20 and -25). Artificial freezing of seeds was carried out in a cooler. After the low temperature tests, the germination tests were completed in the incubator at 25°C in 28 days. After the germination tests, the germination percentages (GP) and mean germination times (MGT) of the seeds were calculated. At the end of the study, the average thousand-grain weight of seeds of all origins was 55.25 gr., the average moisture percentage in air-dried state was 10.3%, the moisture percentage in semi-saturated state was 19.5% and the moisture percentage in fully saturated state was 28.73%. With the increase in the humidity level in the seeds and the decrease in the temperature, the GP values in the seeds decreased in general, while the MGT values increased and there were significant statistical differences between the origins. The germination performance of the seeds was affected at -25 °C (GP 57.7% - MGT 15.9 days) in air-dried seeds, -20 °C (GP 61.3% - MGT 14.2 days) in semi-saturated seeds and -10 °C (GP 45.3% - MGT 18.6 days) in fully saturated seeds. At the temperature level of -25 °C, germination was not observed in seeds with high moisture content. Anamur, Çameli and Bafra origins, which exhibit better germination performance at humidity levels and low temperatures, were determined as frost resistant, while Burdur and Bucak origins were determined as the most durable origins. In the study, germination values in air-dried and semi-saturated seeds (between 10% - 20% moisture content) at temperatures of -5 and -10 °C showed a better performance than the control group. According to this result, applying low temperature stress to the seeds in the relevant humidity ranges without cold stratification for 4-6 weeks can be suggested as a practical method for removing the germination barrier in red pine seeds.