Vegetative compatibility, host range and pathogenicity of Verticillium dahliae isolates in Iran

Abstract

Verticillium wilt is an economically important disease which inflicts serious losses in potato, cotton, alfalfa, some vegetable crops and fruit trees and occasionally ornamentals. Verticillium dahliae, infected cultivated species and weeds were collected from several areas in Iran during tewelve years from 1993-2005 and studied for their vegetative compatibility, host range and pathogenecity. The pathogen was isolated from 27 species belonging to 24 genera and 15 families of plants but was most frequently isolated from Solanaceae, Cucurbitaceae, Oleaceae and Rosaceae hosts. The morphology of V. dahliae isolates on C and water agar media were different especially for micosclerotial appearance time (4-19 days), pigmented zone of colony (37.8-48.33 mm) and microsclerotial morphology (abundant, irregular and elongated shaped or more spherical and scattered). The ratio index of length/width of conidia ranged between 2.32 and 2.70 micrometer with an average of 2.43+0.11. Temperature influenced the radial growth ratio of the isolates and the growth response of V. dahliae isolates to temperature in vitro was quadratic. All isolates were categorized in three groups based on pathogenecity tests on differential test plants (cotton cv. Sahel and eggplant cv. local). 548 V. dahliae isolates from different locations and hosts were assigned to vegetative compatibility groups (VCGs) using nitrate-nonutilizing (nit) mutants. A higher frequency of nit1/nit3 mutants (93%) were obtained compared to nitM (7%). 51.1% of the isolates were assigned to VCG4B, 25.9% to VCG2A and 23% to VCG1. The results demonstrated that V. dahliae isolates assigned to VCGs were closely associated with specific pathogenecity within the group/diverse.