Biological control ofPythiuminduced damping-off of beetroot (Beta vulgaris) in the glasshouse

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Abstract
Eight test organisms were assessed in the glasshouse for their ability to suppress damping-off of beetroot, induced by isolates of Pythium deboryanum or P. ultimum. Test organisms were applied as seed treatments (106 propagules/ml in 2% methylcellulose) and the seed was sown in steam-sterilised seedling mix, which had been artificially inoculated with the respective Pythium spp. A comparison was made with a fungicide (captan) seed treatment. The number of emerged seedlings was recorded at 2 weeks and the number of healthy seedlings and seedling dryweight were recorded at 4 weeks. Four of the test organisms (Penicillium raistrickii, P. simplicissimum, Penicillium sp.(a), and Pseudomonas fluorescens) gave a consistently high level of disease control for each Pythium spp. at both 2 and 4 weeks. This is the first record of biocontrol activity exhibited by Penicillium raistrickii and P. simplicissimum. In particular, P. simplicissimum gave complete control of damping-off induced by P. debaryanum and produced a seedling biomass value equal to that of the uninoculated control. In addition, an isolate of Streptomyces gave complete control of damping-off induced by P. ultimum but failed to control P. debaryanum. These five isolates are considered to be the most promising test organisms for further evaluation.