COMPARISON BETWEEN A CULTURE PLATE METHOD AND AN IMMUNOASSAY TO EVALUATE VASCULAR COLONIZATION OF POTATO BY VERTICILLIUM-DAHLIAE

Vascular colonization by Verticillium dahliae of 14 potato (Solanum tu berosum) cultivars was evaluated in field trials by a culture plate me thod and an indirect competitive enzyme-linked immunosorbent assay (IC -ELISA). Whereas the culture plate technique quantifies fungal propagu les, the monoclonal antibody-based immunoassay detects the soluble ant igen, providing an indicator of fungal biomass. Differences in vascula r colonization were evident with both methods; thus, cultivars could b e ranked as susceptible, intermediate, or resistant. Linear regression analysis of means of each cultivar showed correlation coefficients (r (2)) ranging from -0.606 to -0.835. Spearman's rank correlation coeffi cient (r(s)) ranged from -0.65 to -0.91. Estimation by IC-ELISA of vas cular colonization by V. dahliae in potato is as accurate as that by t he culture plate technique, and results can be obtained in 3 days with an approximately 50% reduction in costs of materials and reagents. Th is quantitative immunoassay can be applied in potato breeding programs to evaluate resistance to Verticillium wilt.