Mutagenesis and Tissue Culture for Selecting Phytopthora cactorum-resistant Strawberry (Fragaria xananassa) Plants

The aim of this study was to isolate Phytopthora cactorum-resistant strawberry plants, regenerated from gamma-irradiated explants on a shoot regeneration medium. Three gamma doses (0, 5, 10, 15 krad) were used to irradiate strawberry axillary buds taken from in vitro-grown plants. After irradiation, axillary buds were cultured on a shoot regeneration medium containing 0.75 mg BA/liter and 0.4 mg IBA/liter. Shoot regeneration occurred mainly from axillary buds irradiated with 5 and 10 krad. The highest dose (15 krad) produced few shoots. The shoot regeneration rate was highest at the 50-krad dose. All the regenerated plants were transferred in the greenhouse. The crude extract of P. cactorum, isolated from the strawberry field, was prepared in sterile water; 1 ml of it was put directly in the center of the crown of each of 400 regenerated plants. After 2 weeks, leaves of most of the plants wilted. Only 20 plants survived the first round of selection; they grew slowly when compared with the control and also showed some tolerance to drought. Further investigations are in progress to reconfirm the resistance of selected putative disease-resistant strawberry plants.