Effect of Phytophthora infestans on potato yield in dependence on variety characteristics and fungicide control

The epidemiology of potato late blight (Phytophthora infestans) was observed over the three-years with 110 potato varieties from various maturity groups treated or not treated with fungicides. The determined severity values were transformed into AUDPC coefficients characterizing rate of disease spreading across the crop in connection with varietal characteristics, fungicide application and year effects. The analysis of the pathogen population for the distribution of races virulent to usually used resistance genes indicated non-efficiency of these genes; resistance could only be increased by breeding for polygenically determined horizontal resistance. There were important yearly variations observed for the epidemiology of P. infestans. A correlation was detected between increasing AUDPC value and yield reduction in both fungicide treated and non-treated variants. AUDPC value of the treated variant is to a certain extent positively correlated with the value of the non-treated variant. However, particular interaction between potato genotype and applied fungicide program was shown, which could positively or negatively affect disease course in dependence on the variety.