Relative Tolerance of Nine Olve Cultivars to Pseudomonas savastanoi Causing Bacterial Knot Disease

Reactions of nine olive cultivars inoculated with olive or oleander strains of Pseudomonas savastanoi were evaluated under glasshouse conditions. Two quantitative indices of pathogenicity were used: 1. gall size from standardised inoculations, measured after 2 months; 2. rate of change of gall size with increasing inoculum concentration. These two indices were combined in a single plot that appears to give the best resolution of all data. Responses of olive cultivars to olive strains of P. savastanoi suggest that cultivars Carolea, Koroneiki, Leccino and Pendolino are the most tolerant, and that Barnea, Manzanillo, Picholine, Picual and a South Australian selection of Verdale are the least tolerant. Olive and oleander strains of P. savastanoi differed in virulence, and between-plant variability in reaction to inoculation was noted. Hypersensitive reactions do not appear to be part of mechanisms of tolerance. Olive strains of P. savastanoi affected all cultivars more severely than did equivalent inoculations with oleander strains.