Population Biology of Verticillium dahliae in Potato and Mint

Jeremiah Kam Sung Dung

Verticillium dahliae (Vd) causes Verticillium wilt of potato and mint and both crops can be rotated in the same fields of the Columbia Basin in the Pacific Northwest. Inoculum of Vd can be found in dirt associated with certified potato seed which is imported and planted on a large scale. The incidence and impact of Vd in dirt associated with certified seed tubers on Verticillium wilt and yield was quantified. Most seed lots contained Vd-infested dirt on seed tubers (68%) and in loose dirt associated with seed lot transport (82%). High Vd levels in seed tuber dirt resulted in greater stem sap colonization when Vd levels in field soil was low (P<0.01) and resulted in greater pathogen levels in postharvest field soils (P=0.04). Infested dirt on seed tubers may introduce Vd into production fields and long-term management requires reducing these propagules. Isolates of Vd from mint and potato usually belong to different vegetative compatibility groups (VCGs) which may restrict gene flow and cause genetic differentiation between populations infecting these hosts. Mating-types and microsatellite haplotypes were determined for 286 Vd isolates from mint, potato, and other hosts and substrates. All potato and mint isolates possessed MAT1-2. Genotypic diversity was significantly greater among potato compared to mint isolates. Isolates from mint and potato were significantly genetically diverged. Significant genetic differentiation was not observed between VCG4A and 4B from potato. Overall, Vd populations from mint and potato fit a clonal reproduction model and populations from these hosts are genetically distinct. Potato early dying (PED) can be caused by Vd and pectolytic bacteria in the genus Pectobacterium, which can also cause aerial stem rot of potato. Additive or synergistic interactions between Vd and Pectobacterium may increase disease severity. Symptoms were evaluated in the greenhouse and pathogens were quantified in stems using real-time PCR. PED symptoms caused by P. carotovorum subsp. carotovorum isolate Ec101 or Vd alone were similar. Inoculations with P. wasabiae isolate PwO405 caused aerial stem rot symptoms and high levels of bacteria were observed in stems. Additive or synergistic effects were not observed in plants co-inoculated with Vd and either Pectobacterium isolate.

Population Biology of Verticillium dahliae in Potato and Mint

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