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Effect of Meloidogyne hapla, Alone and in Combination with Subthreshold Populations of Verticillium dahliae, on Disease Symptomology and Yield of Potato. A. E. MacGuidwin, Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706; D. I. Rouse, associate professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 80:482-486. Accepted for publication 30 November 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-482.

Fumigated microplots on Plainfield loamy sand soil were infested with two levels of Meloidogyne hapla and one level of Verticillium dahliae, alone and in combination, in 1986. The inoculum density of V. dahliae was below the threshold for yield loss in earlier studies. Disease symptoms and yields of potato cultivar Russet Burbank grown in the microplots were evaluated in 1986?1988. There was an increase in populations of nematodes but not Verticillium during the 3 yr of the study. Symptoms associated with potato early dying disease were more severe in plots infested with V. dahliae in 1986 and 1988. Only M. hapla reduced tuber yields. By 1988, yields of plots infested with low and high numbers of nematodes were reduced an average of 48 and 70%, respectively, as compared to noninfested controls. Synergistic interactions between M. hapla and subthreshold population levels of V. dahliae were not observed for symptom expression or yield reduction.

Additional keywords: disease complex.