Biological control of root-knot nematodes (meioidogyne spp.) In common bean using bacillus spp.

Abstract

Bacillus spp. were isolated from the surface of healthy bean roots. Greenhouse experiments were conducted to determine the effect of Bacillus spp. on root-knot nematodes and plant growth.Bean plants were treated with Bacillus isolates and nematodes and data on galling, egg mass and biomas were recorded. The isolates tested had varying (P=0.05) effects, with the majority of them reducing galling in beans. Out of 250 isolates evaluated, 93% reduced galling when compared to the control (water) with 12% of them being were more effective than carbofuran. Twenty percent of the isolates were found to promote plant growth. A laboratory experiment was conducted to assess the effect of culture filtrates Bacillus spp on mobility of second-stage Meloidogyne juveniles. Culture filtrates of the twenty Bacillus isolates tested immobilized more than 80% of the juveniles treated. Twenty Bacillus isolates were selected due to their high activity against root-knot nematodes. The isolates were tested under sterile and non-sterile soil conditions. Galling and egg mass indices were lower in sterile soil than in non-sterile soil conditions. Fewer juveniles were recovered from sterile soil than in non-sterile soil. The effect of selected Bacillus isolates on nodulation in beans was determined using nitrogen-free sterile sand in the greenhouse. Nodulation was variably (P=0.05) affected by treatment of bean plants with Bacillus spp. Four out of 20 selected isolates promoted nodulation, eleven isolates had no effect while six isolates suppressed nodulation. Growth promotion was confirmed in 17 out of the 20 Bacillus isolates selected from the preliminary trial. A greenhouse test to assess the effect of combining Bacillus and Rhizobium spp. on root-knot nematode showed varied reactions. Galling index was relatively lower in plant treated with some Bacillus and the rhizobia inoculants. The lowest galling was recorded in XIV plant treated with Bacillus isolate K194 with a mixture of Rhizobium leguminosarum biovar phaseoli and R. tropici. Selected carriers (ondiri peat, filter mud, cow manure, charcoal dust, and compost) and adhesives (methyl cellulose, sugar and gum arabic) were evaluated on their ability to support high Bacillus populations during their application in nematode control. Charcoal dust as a carrier mixed with Bacillus isolates was the most effective in nematode control, while cow manure was the least effective. Application of Bacillus isolates using carriers resulted significant (P=O.05) increased shoot and root weight as compared with the controls. Galling index was low in plants treated with Bacillus isolates using gum arabic and sugar as adhesives. The potential Bacillus spp. as biocontrol agents of root-knot nematode, Meloidogyne spp. and its ability to promote plant growth was demonstrated under greenhouse conditions. These results show that Bacillus spp. can be incorporated in nematode management package. Application of Bacillus spp. in root-knot nematode management would therefore have an added advantage of enhancing nitrogen supply. Further work to determine the effect of these isolates under field condition should be carried out.