Hyaline mutants from Verticillium dahliae, an example of selection and characterization of strains for host–parasite interaction studies

Abstract

The objective of the present work was to select stable well‐characterized strains of Verticillium dahliae that could be used as biological tools in genetic and plant–microbe interaction studies. Hyaline mutants, known for their stability in pathogenicity were chosen for the study. Diversity in pathogenicity was found among hyaline subclones obtained from a defoliating wild‐type clone, but not within those from nondefoliating ones. Most subclones from the defoliating clone had parental pathotypes, but one (V7‐2) exhibited weak pathogenicity. This subclone (V7‐2), together with a highly virulent one (V7‐7) deriving from the same defoliating parent clone (7), were selected for further characterization, because of their differences in pathogenicity. When studied on the basis of their growth requirements, the two subclones expressed marked differences. V7‐7 grew better than V7‐2 over a wider range of temperature conditions. Both subclones grew similarly in media supplemented with NH4 as nitrogen source, but in those with NO3, V7‐7 grew more vigorously than V7‐2 and only the former could grow when NO2 was used. In spite of these differences, the two subclones were found to belong to the same vegetative compatibility group, confirming their genetic proximity. These results highlight the physiological and genetic complexity inherent in V. dahliae. In view of their characteristics, the clones obtained in this study should prove to be valuable tools in furthering the understanding of genetic and host–V. dahliae interactions.