Analysis of antagonistic interactions between Trichoderma isolates from Brazilian weeds and the soil-borne pathogen Rhizoctonia solani

摘要

The soil-borne pathogen Rhizoctonia solani causes diseases on economically important crops worldwide. For many crops, appropriate methods to control the pathogen are currently not available. However, the use of naturally occurring antagonists offers the possibility for sustainable control strategies. Fungi, originally isolated from the rhizosphere of Brazilian wild plants, were analysed regarding their antagonistic activity against Rhizoctonia. A broad spectrum of antagonistic interactions was to beobserved: inhibition of melanin formation in the fungal cell wall, antibiosis as well as mycoparasitism. Furthermore, we characterized the fungal antagonists by their morphology, genotype, and 18S rDNA sequencing which resulted in a high diversity of Trichoderma strains. The survival rate of Rhizoctonia mycelium following an interaction with the antagonists, which was analysed for 31 mycoparasitic isolates, showed high strain specificity and was temperature dependent. The influence on germination of sclerotia in substrate as well as on potato, the production of fungal cell wall-degrading enzymes, and the disease suppressive effect on lettuce were investigated for ten of the most efficient in vitro antagonists. Based on the screening strategy we could select three promising Trichoderma viride antagonists able to inhibit sclerotia germination of Rhizoctonia, to enhance plant growth, and to suppress disease symptoms on lettuce on a statistically significant level.