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Disease Detection and Losses

Effects of Three Soil Types on Potato Early Dying Disease And Associated Yield Reduction. L. J. Francl, Postdoctoral research associate, Department of Plant Pathology, The Ohio State University (OSU), Ohio Agricultural Research and Development Center (OARDC), Wooster 44691; R. C. Rowe(2), R. M. Riedel(3), and L. V. Madden(4). (2)(4)Professor, and Associate professor, respectively, Department of Plant Pathology, The Ohio State University (OSU), Ohio Agricultural Research and Development Center (OARDC), Wooster 44691; (3)Professor, Department of Plant Pathology, OSU/OARDC, Columbus 43210. Phytopathology 78:159-166. Accepted for publication 18 September 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-159.

Potato early dying is a serious soil-borne disease that occurs in many diverse soils in areas of commercial potato (Solanum tuberosum) production. Verticillium dahliae and Pratylenchus penetrans, causal agents in the early dying disease syndrome, were mixed at several factorial levels with Wooster silt loam, Spinks fine sand, or Rifle peat, and placed in microplots at a single location. The effects of soil type on disease development and yield reduction in potato cultivar Superior was measured over two seasons. Disease was measured as the area under the senescence progress curve (A) and day of senescence onset. Disease progress was greater when soils were infested with both pathogens together than when infested with either pathogen alone. Disease progress and senescence onset were more similar among soils than between years. Regression models that used preplant population levels of pathogens as determinant variables explained more variation in A in 1985 than in 1986. Senescence onset at high levels of V. dahliae and P. penetrans was 3235 days sooner than controls in 1985 and 1924 days earlier in 1986. Differences in disease onset and progress between years were associated with a greater soil moisture deficit and higher temperatures in the latter half of the 1986 season. Yield reduction, for separate years and without using measures of disease as predictors, was explained best by the model: Yield = b0 b1(ln[V. dahliae P. penetrans]) b2(ln[V. dahliae]) + b3(P) in which P = 1 if microplots contained Rifle peat and 0 otherwise. There was no evidence of interaction between soil type and pathogen population on yield reduction when years were analyzed separately, although estimates of the beta coefficients differed between years and P. penetrans consistently reduced yields in sand both years when it was the sole pathogen. Tuber yields in 1985 and 1986 were significantly (P<0.01) correlated with A (r = 0.97 and 0.76) and senescence onset (r = 0.92 and 0.76). A discriminant model that classifies yield relative to controls based on pathogen density at planting and had been developed using previously collected microplot data severely misclassified only 8% of these new data from three soil types. This suggests that soil type can be ignored in classifying relative yield reductions due to potato early dying.