Detection of pathotypes of Verticillium dahliae, the causal agent of olive Verticillium wilt in olive orchards of Tarom using Nested-PCR technique

Verticillim wilt is one of the most important olive vascular diseases caused by Verticillium dahliae Kleb. This fungal pathogen prompts wilting، yield loss and eventually death of the infected trees by devastating of their vascular system. The isolates of V. dahliae are grouped، based on the disease symptoms، in two distinct defoliating and non-defoliating pathotypes، although they are morphologically identical. Detection of the pathotype is an important step forward for selecting proper management strategies، especially for screening of resistant cultivars. In this study we used a PCR-based method to detect the pathotype of different isolates of the fungus، collected from Tarom region in Zanjan province. The wood samples collected from the infected olive trees were cultured and purified on solid medium using conventional methods. Total DNA was extracted both from mycelia and from artificially inoculated olive saplings. A nested-PCR assay was performed using specific primer pairs developed for detection of both pathotypes. Based on the size of the PCR products seperated on the agarose gel، most of the isolates (11 out of 12) belonged to the ND pathotype and only one isolate belonged to D pathotype. The results of this research showed that the ND pathotype is probably the most predominantly distributed pathotype of V. dahliae in Tarom region. Because of the high sensitivity of the nested –PCR، it is possible to survey and to detect the fungus Verticillium on olive، shortly after inoculation of the saplings.