Relationships between race-specific and race-non-specific resistance to potato late blight and length of potato vegetation period in various sources of resistance

Late blight is the most destructive potato disease, and there is consequently strong market demand for disease-resistant cultivars. However, potato resistance to P. infestans is strongly associated with late maturity. In this study, the relationships between race-specific and race-non-specific potato late blight resistance and length of the vegetation period were examined in three unselected progenies with various origins of resistance. The vegetation period and late blight resistance of 514 progeny clones were evaluated in laboratory and field tests. The relative area under the disease progress curve (rAUDPC) and auxiliary parameters for the delay of infection onset (ΔT) and disease progression rate (ΔA) were calculated based on field observations. In all examined progenies, late maturity was correlated with foliage resistance to P. infestans in field experiments, but not under laboratory conditions. Regardless of the resistance source, potato late maturity was always correlated with a low disease progression rate, which is typical for race-non-specific resistance. The mechanism underlying this relationship is likely physiological, and both traits are consequences of the same phenomenon, that is, the higher level of race-non-specific resistance resulting from a tendency for late maturation. Race-specific resistance appears to be unrelated to maturity because none of the tested R-genes against P. infestans, with the exception of R1, contributed to a longer vegetation period of the potato plants. However, late maturity of potato plants enhanced the efficacy of the R-genes under field conditions.