BIOLOGICAL CONTROL OF PYTHIUM SP. IN SOIL AND NUTRIENT FILM TECHNIQUE SYSTEMS BY PSEUDOMONAS AERUGINOSA 7NSK2

Abstract

Pythium sp. is a soil fungus that can cause serious seed and root rot in several crops. Pseudomonas aeruginosa strain 7NSK2, a plant-growth promoting rhizobacterum showed an iron-regulated antagonism against Pythium splendens strain 706 in vitro. Pythium splendens strain 706 is a heterothallic strain that produces big chlamydospores or hyphal swellings but is not able to produce zoospores. As Pythium spp. are important pathogens in nutrient film technique (NFT) systems, the possibilities for biological control of this fungus by P. aeruginosa 7NSK2 in NFT were evaluated. By using a marked P. aeruginosa strain (beta-galactosidase positive and kanamycin resistant) it was shown that these bacteria could survive and spread in a NFT system when added to the recirculating nutrient solution or applied to the seed. They were also able to colonize the plant roots. We were unable to obtain an infection with Pythium splendens in NFT by adding the fungus to the nutrient solution or by placing a Pythium infested pot in the gully. A good Pythium infection could only be obtained by mixing the chlamydospores into the substrate. It was shown that the chlamydospores did not spread into the gullies. Also in NFT, seed treatment with P. aeruginosa significantly reduced damping-off. Moreover, additional protection was obtained when the nutrient solution was also inoculated. We are currently working with a zoospore-producing Pythium aphanidermatum strain to further study the epidemiology of Pythium in NFT systems.