Resistance to Late Blight and Yield of Population B3 Potato Selections in Uganda

Population B3 is the most advanced source of horizontal resistance available at the International Potato Centre (CIP). In this population, testing and selection for horizontal resistance to late blight, unlike those previously applied to population A clones, were simplified significantly (P<0.05) due to the absence of known R-genes. This study, conducted in southwestern and eastern Uganda, evaluated 20 selected potato genotypes in Population B3 for late blight resistance and tuber yield. Late blight severities on many of the Population B3 genotypes were lower than on most local cultivars, including the resistant cultivar, Rutuku. Population B3 genotypes performed better when sprayed with fungicide, Mancozeb, but the reduction in late blight severities due to spraying varied with genotype and location. Although spraying did not significantly (P>0.05) increase yields, almost all genotypes gave higher yields with than without spraying, with significant (P