Effect of bacillus subtilis on bean nematodes in Kenya: A laboratory and green house experiment

Abstract

Nematodes have been causing big losses in the yields and quality of crops worldwide. Bacteria are major biocontrol agents. Laboratory and green house experiments were conducted at the University of Nairobi College of Agriculture and Veterinary Sciences to determine the effect of Bacillus subtilis on bean parasitic and free living nematodes. Bacillus subtilis were isolated from soil using procedure by Racke and Sikora in 1992 in the plant pathology laboratory. Identification of Bacillus subtilis was done using biochemical tests outlined by Claus and Berkeley 1986. The green house experiment was arranged in a completely randomized design with 5 replications. It consisted of 5 pots with nematode infected soil and 5 with sterile sand all inoculated with 2ml of Bacillus subtilis. Un-inoculated soil and soil inoculated with Bacillus subtilis K194 were included as negative and positive controls respectively. Bacillus subtilis inoculum was placed in holes and radicals of germinated seeds inserted for the 12 pots and their 5 replications. 5 Bacillus isolates out of 10 were significantly abundant with colony forming units near those of Bacillus subtilis K194, the positive control. 2 isolates significantly increased the numbers of free living nematodes and three significantly reduced numbers of plant parasitic nematodes. Paratylenchus, Tylenchus and Meloydogyne were the most susceptible genera of nematodes. Bacillus subtilis inoculum can be readily applied in the soil to reduce infestation by plant parasitic nematodes while boosting beneficial free living nematodes.