INTERACTIONS BETWEEN VERTICILLIUM DAHLIAE AND POTATO, MINT, MUSTARDS, AND GRASSES

David Wheeler

Verticillium dahliae is a pathogen and endophyte of several hundred plant species. In the Pacific Northwest, several hosts of V. dahliae are grown in the same fields. The first objective of this research was to reconstruct the evolution of V. dahliae populations from sympatric hosts in Washington State. Populations from wilted potato crops were similar to and evolved from those from asymptomatic mustards and barley but were different from those sampled from wilted mint stands. Inoculum movement was detected between populations sampled from potato and asymptomatic hosts. A subset of isolates recovered from mustards and grasses were pathogens of potato and endophytes of brown mustard and barley. V. dahliae is a pathogen and endophyte of several crops in Washington State. Diverse populations of V. dahliae can co-occur in agricultural fields. Most studies, however, make inferences about disease dynamics from experiments where one isolate is used to inoculate one host. The hypothesis that mixed-infections affect host plants was tested. Plant biomass of potato, brown mustard, and barley were not affected (P > 0.05) by co-inoculations with seven combinations of three V. dahliae isolates. Conversely, disease expression and fungal colonization of potato were affected (P < 0.05) by co-inoculation. Each plant selected for a greater proportion of one isolate than the other two, however, in many cases, up to two isolates were recovered from individual plants. Moreover, five putative heterokaryons were recovered from mustard plants. The composition of V. dahliae genotypes present in field soils should be considered when planning experiments or predicting the risk of wilt. V. dahliae co-exists in soil with plant-parasitic nematodes in the genus Pratylenchus. These organisms cause disease alone and together. Expression of wilt symptoms in mint fields were modeled as a function of V. dahliae DNA in soil, Pratylenchus spp. counts, the crop age, and the cultivar. Pratylenchus spp. counts were identified as the most important predictor of wilt symptoms. The age of the crop, cultivar of the crop, and V. dahliae DNA in soil followed Pratylenchus spp. in descending importance. This research underscores the importance Pratylenchus spp. as drivers of wilt in commercial mint fields.

INTERACTIONS BETWEEN VERTICILLIUM DAHLIAE AND POTATO, MINT, MUSTARDS, AND GRASSES

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