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Interaction of Fungal Wilt Pathogens and Potato Blackleg. R. T. Zink, Former Graduate Student, Department of Plant Pathology, North Dakota State University, Fargo 58105. G. A. Secor, Assistant Professor, Department of Plant Pathology, North Dakota State University, Fargo 58105. Plant Dis. 66:1053-1056. Accepted for publication 8 March 1982. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-1053.

A field study was done to determine the effects of combined inoculations with Erwinia carotovora subsp. atroseptica (Eca) or E. carotovora subsp. carotovora (Ecc) and Fusarium sulphureum, F. oxysporum, F. solani, or Verticillium dahliae on the incidence of seed tuber decay and blackleg. Treatments inoculated with Eca resulted in significantly greater seed tuber decay, blackleg, and reductions in stand and yield compared with treatments inoculated with Ecc. No significant differences were observed between the uninoculated controls and treatments inoculated with Ecc for the variables measured. A significant positive correlation existed between the percentage of seed tuber decay and of blackleg stems per plant early in the season. This correlation diminished following postplant inoculations with fungal wilt pathogens. Postplant inoculations with F. sulphureum, F. oxysporum, F. solani, and V. dahliae significantly increased the incidence of blackleg, with no significant effect on seed tuber decay. Of the different pathogen combinations tested, preplant inoculation with Eca caused the most early-season blackleg, and Eca plus V. dahliae caused the most midseason blackleg. The greatest reduction in yield occurred in plots containing seed tubers that were inoculated before planting with Eca plus F. sulphureum. The results of this study indicate that interactions may exist between the blackleg bacterium and the common fungal wilt pathogens of potato. This interaction of combined infection may cause an increased incidence of blackleg over that caused by these pathogens alone.