Late blight is caused by the oomycete Phytophthora infestans and is a major threat to the global potato production. Sárpo Mira cultivar is considered to be highly resistant to P. infestans, to which the Rpi-Smira2/R8 gene is said to contribute the most. From the population of F1 progeny, between five susceptible cultivars and Sárpo Mira cultivar, we selected ten R8 genotypes containing only the Rpi-Smira2/R8 gene using genetic markers and effector agroinfiltration, and exposed them to four P. infestans isolates differing in their aggressiveness, to evaluate the contribution of the Rpi-Smira2/R8 gene to the late blight resistance level. R8 genotypes, together with the corresponding parental varieties, were inoculated with P. infestans isolates as tissue cultures and as whole plants in the greenhouse. Among the tested R8 genotypes, the highest level of resistance was shown by genotype C571, which was comparable to the parental variety Sárpo Mira after inoculation with foreign isolates of P. infestans. In the case of genotype C571, the level of resistance was maintained both in tissue culture inoculation and in inoculation of whole plants in the greenhouse, while the Sárpo Mira cultivar was moderately resistant to aggressive foreign isolates at the level of tissue cultures and completely resistant as a whole plant in the greenhouse. With the research conducted in the scope of the doctoral dissertation, we have shown that the Rpi-Smira2/R8 gene contributes to late blight resistance, however the level of resistance is lower compared to the Sárpo Mira cultivar and under influence of the genetic background.
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