Selection of natural isolates of Trichoderma spp. for biocontrol of Polymyxa betae as a vector of virus causing rhizomania in sugar beet

The soil fungus Polymyxa betae, Keskin, besides being a root parasite, plays a role of a vector in dissemination of Beet necrotic yellow vein virus (BNYVV) causing rhizomania in sugar beet. An alternative to its chemical control is the application of antagonistic microorganisms suppressing proliferation of the fungal vector. In the present work, 66 Trichoderma isolates have been obtained from sugar beet plantations from diverse locations in Slovakia. The ability of the selected isolates to grow at low temperature (10 °C) and to suppress the colonization of roots with P. betae and the multiplication of BNYVV in roots under glasshouse conditions were tested. The roots of sugar beet seedlings growing in the BNYVV-infested soil were analyzed by serological ELISA test using monoclonal and polyclonal antibodies for the presence of BNYVV and checked microscopically for the occurrence of cystosori of P. betae. The efficacy of the selected strains to suppress the proliferation of BNYVV varied on the average between 21 and 68%. On the basis of these tests, candidate strains for practical application in biocontrol of sugar beet rhizomania were selected.