Biological control of the root-knot nematode Meloidogyne incognita on tomatoes and carrots by plant growth-promoting rhizobacteria

In the current study 27 plant growth-promoting rhizobacteria (PGPR) strains were screened for biocontrol activity against Meloidogyne incognita on 6-week old carrot seedlings that were inoculated with a suspension of J2 juveniles five days after treatment with the bacteria. Five of the PGPR strains, namely Bacillus firmus T11, Bacillus aryabhattai A08, Paenibacillus barcinonensis A10, Paenibacillus alvei T30, and Bacillus cereus N10w, caused 86.0, 85.2, 84.6, 81.5 and 82.1% reduction in gall numbers, respectively. In a subsequent greenhouse experiment on carrots, treatment with strain T30 caused a significant reduction in gall index and egg mass index compared to the control. The reduction in gall numbers caused by strain T30 was not statistically different from that obtained with CropGuard (furfural). Treatment with B. aryabhattai A08 gave the best results on tomato, significantly reducing gall index and egg mass index compared to the control. In vitro experiments with all five abovementioned strains resulted in second-stage juvenile (J2) paralyses. Induction of resistance was not observed in a split-root experiment conducted in the greenhouse, suggesting that secondary metabolites produced by the bacterial strains are responsible for the biocontrol activity. It is concluded that the bacterial strains P. alvei T30 and B. aryabhattai A08 have potential as biological control agents of M. incognita on carrots and tomatoes respectively.