Comparison of the course of pathogenesis caused by Verticillium dahliae (Kleb.) and Phytophthora cactorum (Lebert and Cohn) J. Schröt in three strawberry cultivars under in vitro selection

The strawberries are more or less susceptible to Verticillium dahliae and Phytophthora cactorum, that’s why a constant need to expand knowledge about the mechanisms of resistance to diseases caused by these fungi is requied. In the present study, the course of pathogenesis caused by V. dahliae and P. cactorum in three strawberry cultivars, i.e., Elsanta, Feltar and Teresa, was compared under in vitro selection. The results showed that the extent and rate of development of disease symptoms were mostly insignificantly differentiated on subsequent observation dates. The resemblance observed in Verticillium wilt and phytophthorosis course within each microclone suggested the occurrence of a similar genetic mechanism of resistance response to both fungi. The likeness of average susceptibility to both pathogenic fungi evaluated with McKinney Disease Index (DI%) corresponded with the genetic similarity on the DNA level, which was estimated between selected submicroclones resistant to pathogens within each microclone. The microclone most susceptible to V. dahliae and to P. cactorum was Teresa (DI = 34.02%; 43.53%, respectively), whereas the lowest susceptibility to V. dahliae was observed in Elsanta microclone (DI = 29.85%). The microclone Feltar was considered to be the least susceptible to P. cactorum (DI = 19.50%). Moreover, a strong positive correlation was observed for the extent as well as for the rate between the development of both diseases in each microclone. Heritability in a broad–sense (h2bs) of the extent and rate of development of both pathogeneses reached values above 70%, which revealed the strong genetic determination of the resistance response to both pathogens in the analysed cultivars.