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Ecology and Epidemiology

Effects of Pregermination of Pea and Cucumber Seeds and of Seed Treatment with Enterobacter cloacae on Rots Caused by Pythium spp.. Y. Hadar, Department of Seed and Vegetable Sciences, New York State Agricultural Experiment Station, Geneva 14456, Permanent address of the senior author: Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, Israel; G. E. Harman(2), A. G. Taylor(3), and J. M. Norton(4). (2)(3)(4)Department of Seed and Vegetable Sciences, New York State Agricultural Experiment Station, Geneva 14456. Phytopathology 73:1322-1325. Accepted for publication 13 April 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1322.

In this work, we assessed the influence of germination prior to planting on susceptibility of seeds and seedlings to blights caused by soilborne Pythium spp., and determined biological events associated with changes in susceptibility. Cucumber and pea seeds were pregerminated in aerated water until radicle emergence. When pregerminated seeds were planted in soils infested with Pythium spp., disease incidence was greatly reduced relative to nonpregerminated seeds. When pregerminated seeds were planted in the presence of dead seeds or nongerminated pea seeds, more seeds rotted than when pregerminated seeds were planted in their absence. During seed germination in aerated water, 107- 108 bacterial colony-forming units (CFU) were detected per milliliter of water, while approximately 107 CFU were detected per seed. Seeds germinated similarly, but under aseptic conditions, contained 20 or fewer bacteria per seed, while the water in which they were germinated contained fewer than 35 CFU/ml. Aseptically germinated seeds were more susceptible to Pythium spp. than seeds germinated under nonaseptic conditions. Dry seeds of cucumber, peas, and beets treated with the total bacterial population from germinated seeds were protected from rot. When one of these bacteria. Enterobacter cloacae, was used to treat pea, beet, or cucumber seeds, rots caused by Pythium spp. were markedly reduced E. cloacae was the predominant bacterial species isolated from treated seeds 48 hr after planting in field soil. In vitro, E. cloacae formed sheaths of bacterial cells around hyphae of P. ultimum, and lysis of the enclosed hyphae resulted. There was no evidence of production of any diffusable antibiotic to P. ultimum by E. cloacae.

Additional keywords: antagonism, Beta vulgaris, Cucumis sativus, fluid drilling, Pisum sativum.