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 tuberosum) cultivars was evaluated in field trials by a culture plate method and an indirect competitive enzyme-linked immunosorbent assay (IC-ELISA). Whereas the culture plate technique quantifies fungal propa-gules, the monoclonal antibody-based immunoassay detects the soluble antigen, providing an indicator of fungal biomass. Differences in vascular colonization were evident with both methods; thus, cultivars could be ranked as susceptible, intermediate, or resistant. Linear regression analysis of means of each cultivar showed correlation coefficients (r ) ranging from -0.606 to -0.835. Spearman's rank correlation coefficient (r ) ranged from -0.65 to -0.91. Estimation by IC-ELISA of vascular colonization by V. dahliae in potato is as accurate as that by the culture plate technique, and results can be obtained in 3 days with an approximately 50% reduction in costs of materials and reagents. This quantitative immunoassay can be applied in potato breeding programs to evaluate resistance to Verticillium wilt.