Physiological Specialization and Effects of Inoculum Concentration of Fusarium oxysporum f. sp. phaseoli on Common Beans. M. O. Salgado, Former Graduate Student, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. H. F. Schwartz, Professor, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Plant Dis. 77:492-496. Accepted for publication 18 January 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0492.

Physiological specialization of a strain of Fusarium oxysporum f. sp. phaseoli from Colorado was compared to that of other strains from South Carolina (American Type Culture Collection strains) and Colombia on the International Center of Tropical Agriculture (CIAT) bean Fusarium wilt differential cultivars of Phaseolus vulgaris. The Colorado and Colombian strains produced differential reactions and are considered to be distinct races. The Colorado race exhibited the broadest virulence spectrum. Cultivar HF 465-63-1 was highly resistant to all races. Varying inoculum concentrations of the Colorado race changed the expected disease reaction order of the differential cultivars at inoculum densities lower than 10⁶ conidia per milliliter. The variation of cultivar disease reactions to different inoculum densities can lead to a false classification of races.