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ŠUMARSKI LIST 11-12/2021 str. 58     <-- 58 -->        PDF

changes that occur during the germination process which affect the seed physiology are more controllable in the greenhouse environment.
At the same time, the highest germination percentages were determined in the control process both in the greenhouse and in the nursery. Therefore, the highest germination percentages were achieved in autumn sowings both in the greenhouse and in the nursery. In other words, the positive effect of the stratification process on the germination percentage was not revealed in this study. In many studies conducted on different species of maple, it is stated that the stratification process at varying times has a positive effect on the germination percentage (Tillberg and Pinfield 1982; Pinfield and Stutchbury 1990; Suzka et al. 1996; Evans and Blazich 1999; Yang and Lin 1999; Macdonald 2000; Phartyal et al. 2002; Erdo&287;an Genç and Üçler 2020a; Erdo&287;an Genç and Üçler 2020b). Stratification was continued until the first germinant appear in stratification medium. So, there should be no mistake about the applied stratification time. Although it has been stated in many studies on maple species that the stratification process has a positive effect on the germination percentage, obtaining the highest germination percentages in the seeds sown in the autumn without any pretreatment should be concluded that the sowing time, storage time and storage conditions were also extremely effective on the germination percentage in sycamore maple. In other words, it is possible to state that the sowing time, storage time and storage conditions might be caused changes in seed physiology. Hong and Ellis (1996) stated that the storage of seeds is related to properties such as seed shape, weight and moisture content in shedding period and those two important criteria such as seed moisture rate and 1000 seed weight at maturity stage play a determinant role in seed storage in maple species. Phartyal et al. (2003b) indicated that Himalayan maple seed desiccated to 5.91% moisture content had a significant effect on the extension of viability compared to other moisture content levels irrespective of storage temperature. Therefore, 10±2% seed moisture content applied during storage in sycamore maple may have revealed unsuitable moisture content for seed viability during storage. In addition, Phartyal et al. (2003b) also indicated that interaction of seed moisture content, temperature and storage days showed that Himalayan maple seed stored at -5 °C with 5.91% moisture content retained 28.0% viability up to 1275 days.             
The best germination rate in the greenhouse environment was achieved at the 21.0-24.9 °C air temperature level, 17.0-19.9 °C soil temperature level, 63.0-68.9% relative air humidity level and 60.0-67.9% soil moisture level. The fact that germination percentages vary in both greenhouse and in nursery depending on air temperature, relative air humidity, soil temperature and soil moisture at different sowing times and obtaining a higher germination percentage in autumn sowing compared to spring and summer sowing can be evaluated as the effect of secondary dormancy in sycamore seeds.
In the study, it was observed that mean germination time was faster in the greenhouse in autumn and spring sowings, while the mean germination time in the greenhouse and in the nursery was equal in summer sowing. The highest mean germination time was obtained in summer sowing. It is also stated in different studies that higher mean germination time is achieved in sowings in the greenhouse compared to nursery and the increase in temperature generally increases the mean germination time (Göktürk et al. 2007; Yüksel 2011; Öztürk 2016).
Within the scope of the study, the best germination percentage was obtained in the control process and in the greenhouse environment. In addition, higher germination percentages were obtained in autumn sowing compared to spring and summer sowings. Germination percentage can be increased by performing controlled germination trials under constant temperature and humidity conditions in the greenhouse in autumn. It would be appropriate to choose the greenhouse environment without any pretreatment in the generative mass seedling propagation of sycamore maple. The study was carried out on a single seed family located outside the natural distribution area of the sycamore maple. Population-level studies in natural distribution areas may contribute with different scientific results.
This study was carried for a MSc thesis at Karadeniz Technical University Institute of Science and Technology. Special thanks to Professor Sanda Tomièiæ Gitt for the Crotian translation.
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