Development of a potato seedling assay to screen for resistance to Verticillium dahliae

P>A seedling assay was developed for Verticillium wilt (VW) resistance in potato to provide efficient and rapid screening to identify resistant clones in segregating populations. The method provides uniform inoculum, which may reduce false negatives and the confounding effect of late maturity in field-grown plants. Seedlings of two cultivated varieties, five wild potato families and five families of complex hybrids were tested for VW symptoms after exposure to fungal suspensions and exudate from liquid cultures. The seedlings of the resistant cultivar and two resistant wild species exhibited fewer symptoms in response to fungal suspensions than the susceptible controls, indicating that seedlings can be scored for VW resistance or tolerance. Furthermore, exposure of seedlings to filter-sterilized exudates lacking the fungus elicited symptoms very similar to treatment with cultures containing VW condia. This result suggests that Vd (Verticillium dahliae Kleb.) liquid culture exudates may contain phytotoxins that can cause visible effects on the growth of certain genotypes. Overall, our results indicate that a greenhouse-based seedling assay can be used effectively to identify resistant or tolerant clones.