Evaluation of oleander accessions for resistance to Pseudomonas savastanoi pv. nerii

Nine oleander accessions were evaluated for resistance to Pseudomonas savastanoi pv. nerii, causal agent of the oleander knot disease. None of the accessions was resistant when tested with three bacterial strains of different virulence, but they varied significantly in the severity of symptoms induced by these strains. The most susceptible accessions "Dark Salmon" (dark salmon flower) showed deformation of stems, leaves and seed pods and secondary knots on aerial parts, whereas the least susceptible one "White" (white flower), inoculated with the least virulent strain, showed neither localized knots at the inoculation point nor secondary symptoms. In this study an in vitro test, based on prick inoculation of leaf segments, was optimised for use in pathogenicity tests or as an in vitro resistance screening test.