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Isolation of Pythium oligandrum and other necrotrophic mycoparasites from soil

1985; Cambridge University Press; Volume: 85; Issue: 4 Linguagem: Inglês

10.1016/s0007-1536(85)80257-6

0007-1536

Michael Foley, J.W. Deacon,

Plant Pathogens and Fungal Diseases

Samples of soil and other material from horticultural, grassland, arable, woodland, moorland, fresh-water and coastal sites were assayed for the presence of mycoparasites by incubation on agar precolonized by Phialophora sp. Of the total 164 samples, 84% contained one or more of the mycoparasites, Pythium oligandrum, Trichoderma viride, Gliocladium roseum and an unidentified Pythium sp. (‘Pythium SWO’). P. oligandrum was found in 29% of all samples, 45% of samples from ‘disturbed’ sites (gardens, arable lands, managed grasslands), but only 11% of samples from ‘natural’ sites subject to minimal disturbance (woodlands, moorlands, permanent pastures, coastal sites and fresh-water sediments). It was commonest at pH 5.5.6.5. Pythium SWO was found in 17% of all samples but was probably underestimated because of competition from P. oligandrum on isolation plates. Its distribution was similar to that of P. oligandrum , but it was much less common in horticultural and grassland sites. The mycoparasite P. acanthicum was found only twice, and P. periplocum was not found, although both could grow well on Phialophora -precolonized agar. Overall, mycoparasitic pythia were found in 38% of samples — at a similar frequency to T. viride (45%) and G. roseum (40%). T. viride and G. roseum occurred in similar numbers of ‘naturalrs and ‘disturbed’ sites, and showed different spectra of occurrence from the mycoparasitic pythia, although there was much overlap. In preliminary experiments, pentachloronitrobenzene, chloramphenicol, gallic acid and aureomycin were moderately or markedly inhibitory to both mycoparasitic and non-mycoparasitic Pythium spp. Although a medium containing benzylpenicillin, streptomycin, nystatin and PCNB, with or without rose bengal and gallic acid, selectively isolated Pythium spp. from soil, it did not detect P. oligandrum in a soil known to contain it. Phialophora -precolonized agar plates did so and could be used in a ‘Most Probable Number’ technique to estimate populations of P. oligandrum in air-dry soil.