Detection of Pathogenicity, Measurement of Virulence, and Determination of Strain Variation inPseudomonas syringaepv.syringae

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Abstract
Virulence among strains of P. syringae pv. syringae was compared by leaf and twig inoculation of peach trees (Prunus persica) in the greenhouse. Immature cherry fruit and pear, apple and peach seedlings were also tested as bioassays for pathogenicity and virulence. Lesions induced on cherry fruit correlated poorly with lesions on potted peach trees in the greenhouse, but cherry fruit were capable of detecting pathogenicity in moderately to highly virulent strains. Etiolated pear and apple hypocotyls responded to differences in virulence among strains and showed high correlations with peach tree inoculations in the greenhouse. A bioassay using peach seedling cotyledons was developed for detecting pathogenicity among strains from several host sources and pathovars. Foliar inoculation of peach, apricot, nectarine and plum cultivars with 3 Pseudomonas syringae pv. syringae strains from stone fruit hosts indicated that these strains varied more in levels of virulence than in ability to infect specific hosts.