The potential for host range expansion of Verticillium dahliae by genetic recombination between two pathotypes

Abstract

Verticillium dahliae is a soilborne pathogen that causes wilt diseases of many plant species. Isolates of V. dahliae can be classified into pathotypes, such as the tomato pathotype and sweet pepper pathotype, based on their pathogenicity to each plant. In Japan, only a few isolates that are pathogenic on both tomato and sweet pepper, (tomato-sweet pepper pathotype) have been identified. Our results of RAPD analyses suggested that the tomato-sweet pepper pathotype was genetically related to both the tomato and sweet pepper pathotypes. Therefore, we tested for genetic recombination between these pathotypes of asexual fungus V. dahliae. Conidia were collected from the cocultured nit1 mutant of tomato pathotype and a NitM mutant of sweet pepper pathotype. After culturing these conidia on minimal media, we obtained 22 prototrophic isolates. One of these prototrophic isolates, Prt-D, was pathogenic on both tomato and sweet pepper. Furthermore, RAPD analyses indicated that Prt-D was a genetic hybrid of tomato and sweet pepper pathotype. These results suggest that the host range of V. dahliae may be expanded by genetic recombination between these pathotypes.