Nematicidal effects of the entomopathogenic bacteria Bacillus thuringiensis in soil

Nematicidal effects of five strains of the entomopathogenic bacterium B. thuringiensis were studied in vitro against nematodes extracted from a soddy-podzolic soil and in situ in the soil planted with barley. Nematicidal activity varied among the strains and was associated with either the culture fluid of the bacteria, the cell sediments or the autoclaved cultures. This suggests different nematicidal factors are produced. In in vitro tests the bacterium caused up to 80 % nematode mortality by days 2-4. It was found that, in addition to the known thermo-stable beta-exotoxin, B. thuringiensis can produce thermo-labile factor(s) with nematicidal activity. When barley seeds or soil were treated with living cultures B. thuringiensis, bacterial spores germinated and vegetative cells migrated to the root zone and colonised the root surface of the plants. Irrespective of the treatment types, application of B. thuringiensis reduced a multiplication of nematodes by 1.5 to 3 times as compared to the control. No specific nematicidal activity was found towards separate trophic groups of the nematodes. The application of B. thuringiensis reduced root length and root biomass of the barley plants.