Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 7, 1997
Publication Date: N/A
Interpretive Summary: Silver scurf disease of potatoes cost the potato industry $8.5 million in Idaho alone during the 1992-93 season. It causes browning and shriveling of potatoes and has increased in importance recently, because the disease organism has become resistant to the only fungicide registered for postharvest use on potatoes for human consumption. Biological control of silver scurf should be a feasible alternative to fungicides, but has not been extensively investigated prior to this study. In this study, we isolated potential biological control microorganisms from 12 of more than 50 soil samples that were determined to possess suppressiveness to silver scurf. We discovered that 13 of these microorganisms reduced silver scurf in at least one experiment. The level of control obtained with the most suppressive microorganisms varied with the strain of silver scurf tested. Biological control of silver scurf was obtained, in some cases, without requiring the biological control agent to survive the entire storage period. With continued development, biological control of silver scurf will improve potato quality and reduce the amount of pesticide residues in the environment.
Technical Abstract: Few management strategies exist for silver scurf, an important postharvest disease of potatoes. This study screened the microbiota of 47 agricultural soils and 7 tuber samples for biological control agents of silver scurf. Soil or periderm samples were transferred to separate samples of gamma irradiation-sterilized field soil enriched with potato periderm. After incubation, the samples were assayed for biological suppressiveness to silver scurf using a whole-tuber/infested soil assay. Over 430 isolates of bacteria, yeasts, and actinomycetes were recovered from tubers and soil associated with the 12 most suppressive soil samples. Thirteen strains were selected for further study on three different strains of Helminthosporium solani, including one that was resistant to thiabendazole. Colonization studies with rifampicin-resistant surface was not necessary to reduce disease symptoms. A high amount of variability prevented selection of the single most suppressive strain. Possible sources of variability in biological control are discussed, including physiological age of the tuber, infection in the field, and uneven free moisture in the storage.