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Identification and Control of Major Seed Potato Storage Diseases in Benguet and Mountain Province, Philippines
Dissertation Abstract:
In a four-year survey (1983-86) undertaken to identify major seed potato storage pathogens in Benguet and Mountain Province, Fusarium sambunicum, F. solani, Rhizotonia 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 infected 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 could cause 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.
S. scabies, although frequently observed, was not considered a storage pathogen since it affected only the skin.
To control storage rots in five-month long in-ground storage (IGS) tubes were drenched with fungicides at maturity. Fungicides 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; the joint infection by the two was significantly lower than their separtae infections. Fungicides applied as protectant dip were most effective followed by eradicative dip and protective and eradicative sprats. Protective and eradicative sprays did not differ from each other. As protective dip, benomyl effectively controlled and joint infections by F. solani + R. solani, while thiophanate methyl effectively controlled R. solani. Fungicide application increased yields of large, medium, and total marketable tubers but not the yields of extra-large and small tubers. Treatment with mancozeb and treatments with thiophanate methyl, and chlorothalonil most significantly enhanced the increase in yields of large tubers and medium tubers, respectively. Mancozeb + cymoxanil, benomyl, and mancozeb increased total marketable tubers most significantly.
The use of fungicides with calcium carbide to control rotting by F. solani encountered during the break of dormancy gave promising results. Benomyl effectively controlled F. solani during the incubation period from breaking dormancy to one month exposure of sprouted tubers, and even its latent infection as manifested by the control up to harvest when these tubers were planted. Chlorothalonil, PCNB, and thiophanate methyl likewise provided afequate protection. There was no inhibition of germination in addition to increased yield.