Interactions ofVerticillium dahliae, Colletotrichum coccodes, Rhizoctonia solani,andPratylenchus penetransin the Early Dying Syndrome of Russet Burbank Potatoes

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Abstract
Fumigated microplots were infested with V. dahliae, C. coccodes, R. solani (AG-3) and P. 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.