Genetical variation for resistance to Alternaria solani in an advanced population of potatoes

Eighteen clones, selected over three seasons for resistance to Afternaria solani, were evaluated in San Ramon, Peru (warm tropics), to determine their general combining ability for resistance to the diseases, earliness and yield per plant, using a North Carolina design II. Six susceptible and six resistant varieties were included as controls. Narrow sense heritability (h²) and genetic components of the variance were estimated, both for the North Carolina design II population, and for the advanced clones and resistant controls. Outstanding parents for the transmission of resistance were the clones C85.003, C85.008, C85.009, C85.051 and C85.144. Narrow sense heritability in the North Carolina design II population was 0.44, while in the population of the advanced clones and resistant controls h² was 0.31. The increased levels of resistance found and the rapid reduction, after selection, of the heritability values from about 0.7–0.8 in the starting population of the CIP breeding programme (Mendoza, Martin & Brandolini, 1987a), linked to a decrease in the additive variation, suggest a good breeding efficiency. The introduction of new resistant genotypes and the use of recurrent selection with progeny testing might further enhance the high levels of resistance to A. solani in this population.