Comparison of polymerase chain reaction based methods with plating on media to detect and identify verticillium wilt pathogens of potato

A polymerase chain reaction (PCR) based assay that utilizes specific primers was compared with assays involving plating on selective agar media for its ability to detect and identify verticillium wilt pathogens of potato following artificial inoculations under field conditions. The common Verricillium species were detected in stem tissues and soil using both methods. The PCR assay was faster and efficient, requiring only 2 days for positive species identification, whereas the media-plating method required more than 4 weeks. Verticillium albo-atrum strain 1 (VA1) was the most frequently recovered species in soil and stems that were assayed using PCR and plating methods. However, the weakly pathogenic I! albo-atrum strain 2 (VA2) could not be differentiated from the more aggressive VA1 strain using the plating on media method. Verticillium tricorpus was detected at very low levels in plots that had been inoculated with this species, whereas VA2 was not detected in assayed potato stems using either method. However, both species were readily detected in soil samples, indicating that they survived and proliferated in the soil. The results from this study show that VA1 was the most aggressive strain of verticillium wilt of potato. The PCR assay can rapidly and reliably detect the major Verticillium species in planta and in the soil. Therefore, it is recommended that the PCR method be adopted for routine diagnosis of Verticillium species and for epidemiological studies of verticillium wilt and premature senescence of potato.