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

Four components of partial resistance to Phytophthora infestans were m easured after inoculation in the greenhouse and in the field of Solanu m arnezii x hondelmannii, S. berthaultii, S. circaeifolium, S. leptoph yes, S. microdontum, S. sparsipilum, S. sucrense and S. vernei, and fo ur hybrid progenies of S. microdontum with S. tuberosum. The four comp onents were infection efficiency, lesion growth rate, generation time and sporulation capacity. The results were compared with resistance ra tings derived from field experiments, and with observations made on th e 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 s pecies. In S. microdontum, generation time, infection efficiency and l esion growth rate, and in S. tuberosum infection efficiency, lesion gr owth rate and sporulation capacity appeared positively associated, but in other species no such association was found. A strong hypersensiti ve reaction, the expression of which appeared to depend on environment al conditions, was found in S. microdontum. For S. berthaultii, infect ion efficiency appeared to be the main resistance component.