Evaluation and analysis of reduction of late blight disease in a diploid potato progeny

The rate of late blight disease was analysed for individuals of a diploid S olanum phureja-Solanum tuberosum dihaploid hybrid population (PD), using th ree different assessment techniques, in the laboratory, screenhouse, and fi eld. These hybrids expressed low disease rates in the field, comparable to resistance based on intact R genes. However, none of the parents of PD expr essed any R genes and the pattern of segregation within the PD population w as not indicative of R-gene inheritance. The foliage (or leaflet) area dise ased had the largest broad-sense heritability of all criteria analysed, in all tests performed. In the field evaluations, the PD population showed int ermediate levels of broad-sense heritability for foliage area diseased, rel ative to the much larger heritability detected for the group of controls po ssessing R genes. Resistance in the field of the PD hybrids had very little genotype-environment (G x E) interaction, indicating stability of its expr ession. All genotypes without R genes exhibited heritable, reduced rates of late blight disease in the field, but they were susceptible with low herit ability in screenhouse and laboratory tests. This differential expression o f disease indicates that the plants' indirect response to unknown environme ntal stress in the field may have been measured. The value of the PD hybrid s for breeding of late blight resistant potato and the use of the disease r ate data for detection of the underlying quantitative trait loci are discus sed.