Genetic aspects of resistance to Pseudomonas solanacearum E.F. Smith in potato

The genetic control of resistance toPseudomonas solanacearum in potato is complex and may involve both genes with major effects and genes with minor effects. However, no evidence of a gene-for-gene relationship between the host and the pathogen has been as yet documented. Strain specificity in the potato-P. solanacearum pathosystem is of the polygenic quantitative type and is probably a reflection of differential adaptation of host genotype and pathogen genotype to environments. Thus the resistance is chacterized by strong host x pathogen x environment interaction and tends to break down whenever faced with environmental conditions the host is not well adapted to. Expression of the resistance is heavily dependent on the adaptive potential of the carrier host genotype to a particular environment. Under heat stress conditions, heat tolerance strengthens expression of resistance. Interaction between genes for resistance and genes for adaptation was evident. In the inheritance of resistance, both additive and non-additive gene actions are significant. The relative magnitudes of the estimates of genetic variance components indicated that non-additive gene effects are more important. The narrow-sense heritability of resistance is low, but broad-sense heritability is relatively high. This indicates that clonal selection would be successful in developing clonal cultivars, but progress in population improvement would be slow.