Stability of late blight resistance in population B potato clones

Summary Increased virulence associated with fungicide resistance and variablePhytophthora infestans populations has been recorded in many potato growing regions with enormous economic effects. The current emphasis on disease management in East Africa includes the use of potato varieties with durable resistance to late blight. Seven promising clones from Population B with quantitative resistance (no R-genes), two advanced clones from Population A (with Rgenes) and three control varieties were grown for three cropping seasons in order to determine their reaction and stability of late blight resistance. Late blight occurrence was detected in all cropping seasons. The analysis of variance of disease data (AUDPC) for genotypes, locations x seasons was highly significant (P<0.001) indicating the differential response of the geno-types and the need for stability analysis. The Additive Main Effects and Multiplicative Interaction (AMMI) statistical model, showed that the most stable genotypes were 392127.256, 381471.18, 387121.4 (resistant) and 391049.255 (susceptible to late blight). Within environments, the ranking of genotypes was not consistent. The variety Kabale was ranked as the most susceptible genotype while clone 381471.18 and Rutuku were ranked the most resistant. Selective deployment of resistant and stable varieties is critical in minimizing economic loss and damage attributed to late blight in low input farming systems.