Biocontrol efficiency of Bacillus thuringiensis toxins against root-knot nematode, meloidogyne incognita

The toxin proteins produced by Bacillus thuringiensis (Bt) are the most broadly used natural insecticides in agriculture. To investigate the potential use of vegetative and crystal toxins to control parasitic nematodes, we studied the nematicidal effect of Bt toxins against root-knot nematode. Nematicidal effects of spore/crystal proteins (SCP) of ten Bt isolates were studied in vitro against Meloidogyne incognita nematode. The spore/crystal proteins of isolates Bt7N, BtDen, Bt18, BtK73, BtSoto and Bt7 showed the highest nematicidal activities, with the mortality range of 86-100%. In addition, ammonium sulfate cut-off fraction of vegetative cultures of the most potent isolates (Bt7, Bt7N, BtSoto and BtDen) was examined in vitro for their nematicidal effects. The observed mortalities of Bt7N and Bt7were 100 and 89.4% for 80% ammonium sulfate cut-off respectively. The culture fluid (CF), cell-free supernatant (CFS) and cell-pelleted residues (CP) of each of the four isolates (Bt7, Bt7N, BtSoto and BtDen) were evaluated for their nematicidal activities in vivo, using tomato plants as a host. The results demonstrate that both crude suspension (CS) and cell-free supernatant (CFS) of isolate Bt7N reduced the number of egg masses by 78% and 77% respectively, and number of eggs by 84% and 76% compared to control.