Effect of various lengths of cold stratification period on the germination of wild service tree (Sorbus torminalis) seed samples harvested in the Czech Republic

The paper deals with the assessment of the influence of the length of cold stratification period on the germination parameters of seeds of wild service tree [Sorbus torminalis (L.) Crantz]. The germination tests (4 × 100 seeds) were conducted in two runs in 2020 and 2021; they were performed for three seed lots and three cold stratification periods (two, three and four months) before the testing of germination in each run. The values of germination energy and germination capacity were assessed, and the germination rate was computed. The results showed that the two-month cold stratification period has not been sufficient to overcome the dormancy of tested seeds. Regardless of the year in which the tests were conducted, seeds stratified for two months showed almost zero germination. For seeds treated with three- and four-month cold stratification, the germination percentage varied from ca. 5% to 32% and from ca. 13% to 46%, respectively. Our results basically correspond with findings reported in the reviewed literature. In 2020, the seeds subjected to four-month stratification performed significantly better than the seeds subjected to three-month stratification. However, in 2021, the seeds stratified for three months reached slightly better results. Four-month stratification also led to an increased percentage of prematurely germinated seeds during stratification. To conclude, the two-month period of cold stratification proved to be insufficient and at least three months of cold stratification are needed to obtain the adequate germination of seeds in subsequent laboratory tests.