Early drought test on seeds of some Turkish Red Pine (Pinus brutia ten.) provenances collected in different years

In this study, seed traits and germination responses under drought stress were determined in seeds of Turkish red pine (Pinus brutia Ten.) collected from three different provenances (TB-13, TB-20, and TB-38) over multiple years. Thousand-seed weight, moisture content, seed diameter, and seed length were measured, and germination tests were conducted using polyethylene glycol (PEG-6000) at water potentials of 0, -0.2, -0.4, -0.6, and -0.8 MPa. Thousand-seed weight ranged from 41.5 to 60.7 gr, seed diameter from 3.89 to 4.55 mm, and seed length from 6.34 to 7.10 mm. The TB-38 provenance exhibited higher seed diameter and length, whereas the TB-20 provenance showed higher thousand-seed weight. Seed moisture content varied between 7.04% and 9.97% and differed according to the year of collection. With increasing drought stress, germination percentage (GP), relative germination percentage (RGP), and germination rate (GR) generally decreased across all provenances. Statistical analyses indicated that the reductions in RGP and GR were significant. Analysis of variance revealed significant effects of provenance, collection year, drought stress, and their interactions on RGP and GR (p < 0.05). In this context, the Kaş provenance exhibited higher germination performance under low to moderate drought stress, whereas the Serik provenance was relatively more tolerant under high drought stress conditions. Differences observed among collection years within provenances indicate that germination performance is influenced not only by genetic background but also by environmental conditions during seed development. The significant year × drought stress interaction further suggests that germination responses to drought stress vary depending on the collection year. Although these differences were statistically significant, overall trends in RGP and GR at the same drought stress levels were largely maintained, and values remained close across years. The findings indicate that early-stage drought responses in Turkish red pine seeds reflect genetically based adaptive differences among provenances, while also being shaped by short-term physiological responses induced by environmental conditions associated with the year of seed collection.