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 primer s was compared with assays involving plating on selective agar media for it s ability to detect and identify verticillium wilt pathogens of potato foll owing artificial inoculations under field conditions. The common Verricilli um species were detected in stem tissues and soil using both methods. The P CR assay was faster and efficient, requiring only 2 days for positive speci es identification, whereas the media-plating method required more than 4 we eks. Verticillium albo-atrum strain 1 (VA1) was the most frequently recover ed species in soil and stems that were assayed using PCR and plating method s. However, the weakly pathogenic I! albo-atrum strain 2 (VA2) could not be differentiated from the more aggressive VA1 strain using the plating on me dia method. Verticillium tricorpus was detected at very low levels in plots that had been inoculated with this species, whereas VA2 was not detected i n assayed potato stems using either method. However, both species were read ily detected in soil samples, indicating that they survived and proliferate d in the soil. The results from this study show that VA1 was the most aggre ssive strain of verticillium wilt of potato. The PCR assay can rapidly and reliably detect the major Verticillium species in planta and in the soil. T herefore, it is recommended that the PCR method be adopted for routine diag nosis of Verticillium species and for epidemiological studies of verticilli um wilt and premature senescence of potato.