Document Type : Research Paper
Authors
Research Institute of Forests and Rangelands
10.22092/ijrfpbgr.2026.372335.1493
Abstract
Background and Objectives: Thymus daenensis Celak. is one of the most valuable medicinal and aromatic plants native to Iran. Excessive harvesting from natural habitats, prolonged drought, and recurrent rangeland fires have seriously threatened many native and endemic thyme populations. Owing to its high adaptability to harsh environmental conditions and its high essential oil content, T. daenensis is considered a promising species for rangeland restoration and cultivation in marginal lands affected by water scarcity and poor soil fertility. Successful domestication, cultivation, and ecological restoration using this species require the identification of appropriate seed storage conditions that maintain seed viability and maximize germination. Since seed longevity is strongly influenced by initial seed quality and storage conditions, determining the optimum storage temperature is essential for both farmers and gene banks to minimize seed deterioration and preserve seed quality during storage.
Materials and Methods: The plant material consisted of seeds collected from two natural populations of Thymus daenensis originating from Fereydunshahr (Isfahan Province) and Lanjrud (Markazi Province), Iran. Seeds were harvested from cultivated plants in September 2022, dried under shade, and stored in paper bags. The effects of storage temperature and storage duration on seed germination characteristics were evaluated using a factorial experiment arranged in a completely randomized design with three replications. Treatments consisted of seven storage periods (0, 1, 2, 3, 4, 15, and 18 months) and three storage temperatures (ambient laboratory temperature, +4°C, and −18°C). Germination percentage, germination rate, mean germination time, seed vigor index, root length, shoot length, and root-to-shoot length ratio were recorded. Data were subjected to analysis of variance, and treatment means were compared using Duncan’s multiple range test in SAS software.
Results: A significant interaction was observed between storage temperature and storage duration for most germination traits. In the Fereydunshahr population, initial germination immediately after harvest was 59%, which increased after three months of storage to 84%, 91%, and 79% under ambient temperature, +4 °C, and −18 °C, respectively. After 18 months of storage, germination percentages were 61%, 81%, and 83% under the respective storage conditions. For short-term storage intended for planting in the following growing season, seeds stored at +4°C exhibited significantly higher germination percentage, seedling length, and seed vigor index than those stored under ambient conditions or at −18 °C. In contrast, for long-term storage (up to 18 months), −18 °C proved to be the most effective storage temperature for maintaining seed quality, whereas ambient temperature resulted in the greatest decline in seed performance. In the Lanjrud population, initial germination was 100%, and no substantial differences were observed among the three storage temperatures during either short-term or long-term storage, indicating excellent seed longevity and storage stability in this population.
Conclusion: The results demonstrated considerable variation in post-maturation behavior and storage response between the two populations of T. daenensis. Dry storage significantly improved seed germination, particularly in the Fereydunshahr population. For short-term storage (approximately three months) intended for sowing in the subsequent growing season, storage at +4 °C is recommended because it provides the highest germination percentage, seedling growth, and seed vigor. Therefore, farmers are advised to store thyme seeds under refrigerated conditions rather than at ambient temperature. For long-term conservation, storage at −18 °C provided slightly better seed viability than storage at +4 °C. Although this difference was relatively small, it may become economically important for large-scale seed production and long-term germplasm conservation. Consequently, −18 °C is recommended for long-term storage in gene banks and commercial seed storage facilities, whereas +4 °C is adequate for routine short-term seed storage and subsequent field planting.
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