COMPONENTS OF RESISTANCE TO LATE BLIGHT (PHYTOPHTHORA-INFESTANS) IN 8 SOUTH-AMERICAN SOLANUM SPECIES

Four components of partial resistance to Phytophthora infestans were measured after inoculation in the greenhouse and in the field of Solanum arnezii x hondelmannii, S. berthaultii, S. circaeifolium, S. leptophyes, S. microdontum, S. sparsipilum, S. sucrense and S. vernei, and four hybrid progenies of S. microdontum with S. tuberosum. The four components were infection efficiency, lesion growth rate, generation time and sporulation capacity. The results were compared with resistance ratings derived from field experiments, and with observations made on the potato cultivars Bintje, Bildtstar, Libertas and Pimpernel. Genetic variation for all components was found, while the relative importance of the components of partial resistance appeared to vary between the species. In S. microdontum, generation time, infection efficiency and lesion growth rate, and in S. tuberosum infection efficiency, lesion growth rate and sporulation capacity appeared positively associated, but in other species no such association was found. A strong hypersensitive reaction, the expression of which appeared to depend on environmental conditions, was found in S. microdontum. For S. berthaultii, infection efficiency appeared to be the main resistance component.