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Postharvest Pathology and Mycotoxins

Soft Rot Susceptibility of Potatoes with High Reducing Sugar Content. Victor Otazu, Former graduate student, Department of Plant Pathology, North Dakota State University, Fargo 58105, Present address of senior author: Consortium for International Development, Casilla T229, Cochambamba, Bolivia; Gary A. Secor, assistant professor, Department of Plant Pathology, North Dakota State University, Fargo 58105. Phytopathology 71:290-295. Accepted for publication 17 July 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-290.

A highly significant correlation (r = 0.65) was obtained between reducing sugar (RS) content and soft rot severity in Norgold Russet potato tubers of various ages held at different storage temperatures. Tubers cool stored at 3–6 C had elevated levels of RS and developed more soft rot per tuber than did tubers warm stored at 21–26 C that had lower amounts of RS. Reconditioned tubers (warmed after cool storage) developed an intermediate amount of soft rot. Similarly, stem-end tuber parts with higher RS content developed more soft rot than did bud ends containing lower amounts of RS. When inoculated tubers were incubated in mineral oil or water, significantly more soft rot developed in water-immersed tubers irrespective of RS content. Oil immersion of tubers had no effect on soft rot development compared to that in nonimmersed tubers. Wound inoculation of tubers of Norgold and a relatively low-RS cultivar, Norchip, resulted in less soft rot in Norchip. However, lenticel infection was more severe in Norchip, which implies two types of soft rot susceptibility/resistance in potatoes. Soft rot severity as well as RS content during various points of a tuber “life cycle” are shown. The significance of RS in tubers is discussed in relation to soft rot development and in view of contrasting evidence reported from in vitro studies showing polygalacturonase transeliminase repression by glucose.