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The effect of preculturing in vitro plantlets of two strawberry (Fragaria ×ananassa Duch.) cultivars grown on micropropagation medium with and without hormones on regenerating shoots from leaf disks was examined. Preculturing stock plants on micropropagation medium with hormones (BAP at 0.5 mg·liter-1 + IBA at 0.5 mg·liter-1 GA, at 0.2 mg·liter-1) promoted shoot regeneration in the two cultivars tested. Using hormone-containing micropropagation medium for preculture, the highest mean regeneration rate of 9.9 shoots per total number of leaf disks was obtained for the Finnish cultivar Hiku on modified Murashige and Skoog (MS) regeneration medium supplemented with (in mg·liter-1) 2000 KNO3, 400 casein hydrolysate (CH), 3 BAP, and 0.1 IBA. For the Norwegian cultivar Jonsok, the highest mean regeneration rate of 12.8 shoots per total number of leaf disks was obtained on modified MS regeneration medium with (in mg·liter-1) 600 CH, 3 BAP, and 0.1 IBA. Chemical names used: 6-benzylaminopurine (BAP); 3-indolebutyric acid (IBA); gibberellic acid (GA).
The occurrence of bacteria in different tissues was studied using field-grown strawberries, in vitro-grown strawberries, wild strawberries, and aseptically germinated strawberry seedlings. Strawberry has a number of endophytic bacteria in its the internal tissue, most of which appear to be nonpathogenic. In the in vitro-grown strawberries, all identified isolates were in the genus Pantoea. In field-grown garden and wild strawberries the most common genera were Pantoea and Pseudomonas. Location of eubacterial inhabitants within strawberry tissue sections was studied by in situ hybridization. Bacteria were detected in flower stalks, leaf stalks, leaves, stolons, berries and aseptically germinated seedlings. The existence of bacteria in seeds and seedlings suggests that bacteria are able to move up to the generative tissue and, ultimately, to the next generation, forming a symbiosis-like chain of plant-bacteria coexistence.