VIEW ARTICLE

Relationship of Isolate Source to Virulence of Pseudomonas syringae on Phaseolus vulgaris. S. M. Saad, Project Associate, Department of Plant Pathology, University of Wisconsin, Madison 53706; D. J. Hagedorn, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 62:678-680. DOI: 10.1094/Phyto-62-678.

Virulence of 30 Pseudomonas syringae isolates from 11 hosts and six geographic locations was compared on bean cultivar Tenderwhite in the greenhouse using inoculum levels of 10³ and 10⁸ cells/ml. All bean and lima bean isolates tested at both inoculum levels induced typical olive-green, water-soaked lesions within 3 to 4 days at 22 C. These lesions soon became necrotic with marginal chlorosis. Isolates from pear, apple, sour cherry, lilac, plum, peach, walnut, and sorghum produced only tiny dark necrotic flecks within 24-48 hr with inoculum containing 10⁸ cells/ml, but no macroscopic symptoms were obtained with the lower inoculum level. The logarithmic growth in bean pods was similar for P. phaseolicola race 1 and isolates of P. syringae from bean, pear, lilac, and sorghum. However, between 2 and 4 days after inoculation, the population of P. phaseolicola and the bean isolate continued to increase, but at a slower rate, whereas the populations of the other isolates declined. These studies indicate a positive relationship of virulence to bean with P. syringae isolate from snapbean and lima bean only.