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Virulence of Verticillium dahliae and V. albo-atrum Isolates in Tomato Seedlings in Relation to Their Host of Origin and the Applied Cropping System. E. C. Tjamos, Research plant pathologist, Laboratory of Mycology, Plant Pathology Section, Benaki Phytopathological Institute, Kiphissia, Athens, Greece; Phytopathology 71:98-100. Accepted for publication 15 July 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-98.

The pathogenic variation of 334 Verticillium dahliae and V. albo-atrum isolates in tomato seedlings was investigated. Disease severity assessed by symptom development and host colonization, showed that strains isolated from 27 plant species with a widespread distribution in Greece, varied from nonpathogenic to highly virulent on the susceptible tomato cultivar Early Park. The degree of pathogenicity to tomato was seldom related to the plant species from which the isolate was obtained, but was dependent on the previous cropping history. Isolates obtained following monoculture of nonsolanaceous hosts were nonpathogenic or mildly pathogenic while isolates originating from areas of a diversified cropping system, including tomatoes and other vegetables, generally were highly pathogenic to tomato.