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Interactions of Verticillium dahliae, Colletotrichum coccodes, Rhizoctonia solani, and Pratylenchus penetrans in the Early Dying Syndrome of Russet Burbank Potatoes. J. B. Kotcon, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address of the senior author: Long Island Horticultural Research Laboratory, Riverhead, NY 11901; D. I. Rouse(2), and J. E. Mitchell(3). (2)(3)Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 75:68-74. Accepted for publication 29 June 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-68.

Fumigated microplots were infested with Verticillium dahliae, Colletotrichum coccodes, Rhizoctonia solani (AG-3), and Pratylenchus penetrans singly and in all possible combinations in a replicated factorial experiment. Russet Burbank potatoes were used in each experiment. The amount of root colonization by each of the pathogens, stem colonization by V. dahliae and C. coccodes, visual symptoms of disease, amount of root and foliage growth, and final tuber yield were determined in 1980 and 1982. In 1983, visual symptom and final yield data were collected. Stem colonization by V. dahliae was a more sensitive measure of soil infestation by V. dahliae than was the amount of root colonization. Symptom severity, scored on a 0- 5 scale, was significantly greater in treatments containing V. dahliae than in treatments not containing V. dahliae. Plants in treatments containing V. dahliae had reduced root growth, foliage weight, and tuber yield. P. penetrans caused stunting, chlorosis, and premature senescence but did not reduce yield. C. coccodes and R. solani had no direct effect on disease symptoms, plant growth, or yield. Interactions of P. penetrans, C. coccodes, or R. solani with V. dahliae did not result in significant yield reductions. Effects of P. penetrans in combination with V. dahliae on symptom expression were additive.

Additional keywords: disease complex, soilborne plant pathogens, Solanum tuberosum.