METHODOLOGICAL BASE OF STRAWBERRY BREEDING IN RUSSIA FOR FUNGAL PATHOGEN RESISTANCE
Before the beginning of our investigations in 1961, there was no strawberry breeding program for immunity in the USSR. It was not possible at that time incorporate multiple resistance to diseases because there were no methodological or genetic programs concerning this aspect and specific pathogens were not reliably determined. Our investigations determined the major strawberry diseases: Verticillium wilt (Verticillium dahliae Kleb.), red stele root rot (Phytophthora fragariae Hickm.), white spot [Mycosphaerella fragariae (Tul.) Lind.], leaf scorch [Diplocarpon earliana (Ell. & Ev.) Wolf], leaf blotch [Dendrophoma obscurans (Ell. & Ev.) Anderson], powdery mildew [Sphaerotheca macularis (Wallr. ex Fr.) Jacz.], gray mold (Botrytis cinerea Pers. ex Fr.), and leather rot [Phytophthora cactorum (Lib. & Cohn.) Schroet.].
Regional differences were observed in disease severity and pathogen physiology. Specific and race specialization of pathogens (especially Verticillium sp.) was studied. The working collection was formed comprising more than 1,500 isolates of seven Verticillium species, cultured from 19 plant species from the main Verticillium zones of our country. We found that in the Northern Caucasus, Verticillium wilt is mainly caused by V. dahliae Kleb. and only sometimes by V. albo-atrum Reinke & Berth. and V. lateritium Berth. Specific and race specialization of V. dahliae was experimentally determined. All V. dahliae isolates from strawberry, tomato, peper, and eggplant were virulent in strawberry and vice versa (Table 1), indicating very little pathogenic specialization. This made it unlikely to find physiological races. However, 10 year multiple experiments of strawberry variety inoculations with V. dahliae isolates allowed us to show for the first time six physiological races of this fungus on strawberry, to show their diversity, territorial suitability and potential distribution of each race.