Impact of Multi-year Cropping Regimes on Solanum tuberosum Tuber Yields in the Presence of Pratylenchus penetrans and Verticillium dahliae.

Five cropping regimes involving combinations of 2 legumes, alfalfa (Medicago sativa) and yellow sweet dover (Melilotus officinalis), 2 monocots, corn (Zea mays) and sudax (Sorghum halupeuse x Sorghum sudanese), and potato (Solanum tuberosum cv. Superior) were tested for their impact on potato yields in a field infested with Pratylenchus penetrans and Verticillium dahliae. No differences in 1990 tuber yields were observed among the five cropping regimes (P < 0.05). In 1991, yields following 1 year of corn, sudax, sweet clover, or alfalfa and 2 years of potato were not different from that of 3 years of continuous potato (P < 0.05). Two years of sweet clover or alfalfa followed by potato resulted in significantly increased potato tuber yields compared with 3 years of potato (P < 0.05). The 2-year legume and 2-year grain rotations resulted in lower P. penetrans population densities at the end of the 3-year rotation compared with 3 years of continuous potato (P < 0.01). The highest preplant V. dahliae population density (34 cfu/g soil), together with a P. penetrans density of 12/100 cm(3) of soil was in the sudax-sudax-potato cropping regime and resulted in the lowest potato tuber yield. The highest preplant P. penetrans population density (54/100 cm(3) soil), together with a V. dahliae population density of 19.5 cfu/g soil was observed in the corn-corn-potato cropping regime and resulted in the second lowest potato tuber yield in 1991. After 3 years, potato tuber yields were negatively related to preplant densities of V. dahliae (r(2) = 0.237), P. penetrans (r(2) = 0.175), and both pathogens (r(2) = 0.380). A comprehensive regression model was developed to isolate pathogen effects on potato yields from cropping regime effects encompassing all 10 cropping regimes (r(2) = 0.915).