VARIATION IN RESISTANCE TO PHYTOPHTHORA-INFESTANS AMONG 21 SOLANUM-VERRUCOSUM PLANT INTRODUCTIONS

Detached leaflets of 21 Solanum verrucosum plant introductions (PIs) were inoculated with two races of Phytophthora infestans to evaluate levels of resistance present within this species. Inoculated leaflets were visually evaluated for the percentage area colonized by P. infestans and the intensity of sporulation over the colonized area. Disease reactions ranged from moderately susceptible to highly resistant (immune). Significant plant-to-plant heterogeneity for resistance was observed within many of the PIs, indicating that they may represent mixtures of different genotypes. Hypersensitive flecks were observed on some inoculated leaflets of all PIs tested. Adult plant reactions showed moderate agreement with those obtained by other workers on seedling populations of several PIs. These results support the hypothesis that R-genes and polygenes for resistance to P. infestans exist within S. verrucosum accessions. This species thus may provide a useful source of novel late blight resistance genes. © 1990 Springer.