A root-injection method to assess verticillium wilt resistance of peppermint (Mentha x piperita L.) and its use in identifying resistant somaclones of cv. Black Mitcham

Three studies were initially conducted using five mint cultivars with known disease reactions to verticillium wilt to determine if inoculation method, root-dip as compared to root-injection, had an affect on the plant growth and disease reaction. The planting media did not affect the development of wilt symptoms in susceptible varieties, however, the soil/peat based medium resulted in higher shoot fresh weight at harvest than the perlite/vermiculite medium. Black Mitcham had the highest susceptible disease rating and greatest reduction in fresh shoot weight from inoculation with Verticillium dahliae at two inoculum concentrations, 104 or 106 microconidia/ml. Native spearmint was resistant and Mentha crispa was moderately resistant, whereas, Murray Mitcham peppermint and Scotch spearmint were moderately susceptible to verticillium wilt with a corresponding lower fresh shoot weight. Scotch spearmint was less susceptible at the low inoculum concentration than at a higher level of microconidia, indicating a low level of disease resistance. Overall, the two inoculation methods resulted in similar cultivar responses to verticillium wilt, although the root-injection method was more applicable for large plant populations. Thus, the root-injection method of inoculation was utilized to screen 743 Black Mitcham derived somaclones for wilt resistance, of which nine somaclones were found resistant in repeated inoculation tests.[PUBLICATION ABSTRACT]