Biological Control of Pythium Damping-Off of Cucumbers withPythium nunn: Population Dynamics and Disease Suppression

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Abstract
Addition of Pythium nunn to aerated steamed soil infested with P. ultimum resulted in disease and pathogen suppression. Population densities of P. ultimum and disease incidence decreased as initial inoculum density of P. nunn increased. Disease suppression decreased as initial inoculum density of P. ultimum increased. Suppression lasted longer when inoculum of P. nunn was produced on 1% rolled oats (w/w) than on 0.3% ground bean leaves. Population densities of P. nunn were not affected by population densities of P. ultimum in aerated steamed soil. P. nunn did not increase saprophytically in raw soil unless an organic substrate was added. Cucumbers grown in aerated steamed soil infested with P. ultimum and P. nunn had greater root dry weights than plants grown in soil infested with P. ultimum alone. Cucumber seeds treated with P. nunn and planted in aerated steamed soil infested with P. ultimum had greater percent emergence than untreated seeds planted in the same soil. Evidence indicates that P. nunn requires organic substrates rather than living fungal hosts for antagonism and disease suppression to operate.