Author : Luis, Janet S.

Summary : In a four-year survey (1983-86) undertaken to identify major seed potato storage pathogens in Benguet and Mountain Province, Fusarium sambunicum, F. solani, Rhizoctonia solani, Pseudomonas solanacearum (biovars I and II), disease complex of F. solani + R. solani, and occasionally F. solani with STREPTOMYCES SCABIES were encountered and isolated from diseased tubers. Except for F. sambunicum, all pathogens were consistently present in all survey sites throughout the survey seasons. F. solani was more virulent than F. sambunicum. All pathogens were capable of causing extensive rotting as shown in inoculation experiments. Likewise, these major storage pathogens were carried as latent infections in healthy-looking seed potatoes. Incidence of major storage pathogens was generally higher during the wet season than the dry season. Commonly associated fungi which did not cause rotting when inoculated alone in intact tubers included Asperqillus sp. and Penicillium sp. STREPTOMYCES SCABIES, although frequently observed, was not considered a storage pathogen since it affects only the skin. To control storage rots in five-month long in-ground storage (IGS) tubes were drenched with fungicides at maturity. Fungicide application, however, did not significantly control F. solani, P. solanacearum, and disease complex of F. solani + R. solani. Longer IGS increased the incidence of the major storage pathogens as well as losses in yield. The study on the chemical control of F. solani, R. solani, and joint infections by F. solani + R. solani was more effectively controlled than R. solani and that joint infection by the two was significantly lower than their seperate infections. Fungicides applied as protectant dip were most effective followed by eradicative dip, protective, and eradicative sprays. Protective and eradicative sprays did not differ from each other. As protectant dip, benomyl effectively controlled F. solani and joint infections by F. solani + R. solani, while thiophanate methyl effectively controlled..