The nematicidal potential of local<i>Bacillus</i>species against the root-knot nematode infecting greenhouse tomatoes

Abstract

Bacillus spp. were isolated from Iranian tomato fields and evaluated for their efficacy against root-knot nematodes, Meloidogyne javanica. The 52 spore-forming bacterium isolates were obtained from tomato rhizosphere following heat treatment. Eight isolates were chosen based on their potency in prevention of M. javanica egg hatch and juvenile mortality and production of proteolytic enzymes in Petri plates. Their ability to form biofilms were also determined in pot experiments. According to phenotypic traits and 16s rDNA sequencing, all selected isolates belonged to Bacillus spp. including B. cereus and B. pumilus. Treatment with bacterial culture filtrates in vitro caused juvenile mortality of 72 to 99% after 48 h. After four days, the percentage of egg hatch ranged from 1.6 to 59% depending on the isolate. Bacillus pumilus (ToIr-MA) and Bacillus sp. (ToIr-10) were found to have significant ability to produce extracellular proteases and to form maximum biofilm, considerably reducing the number of egg masses and root gall index (P = 0.05) in comparison to untreated plants. Application of ToIr-MA and ToIr-10 enhanced the fresh and dry weights of shoot and root systems. There was significant enhancement in dry root weight (45 and 50%) and shoot weight (67 and 75%). Results suggest that these two Bacillus spp. have potential as biocontrol agents against root-knot disease in tomato production.