Screening of antagonistic bacteria to root-knot nematode Meloidogyne incognita

Root-knot nematodes are an economically damaging parasite of many crop species. Chemical nematicide is ineffective in the sedentary stage of the nematode as well as harmful to health and the environment. Antagonistic bacteria can provide effective and environmentally safe management of this pest. The objective of this study was to select antagonistic bacteria to M. incognita under laboratory and greenhouse environments. A total of 268 isolates of rhizo-and endophyte bacteria were screened by means of applying bacterial cells to multi-well plates containing eggs or J2 stage of the nematode. Thirty-four isolates could cause 70.5–97.9% of egg hatch failure and 12 isolates killed 76.2−95% of J2. Biosafety assessment by means of a hypersensitive reaction test on tobacco leaves and hemolytic test on blood agar resulted in 11 isolates with no indication of plant and mammalian pathogenic properties. Subsequent pot experiments on tomato plants by means of soil drenching with bacterial cell suspension obtained one rhizobacteria isolate (AA1) that significantly reduced root gall score to 1.6 and two rhizobacteria (ZR3.1 and AA2) that were comparably effective to nematicide in reducing root gall score i.e., 2.9, 3.2, and 3.3, respectively. The 16S rRNA gene sequencing of a selected isolate indicated that AA1 had 98.6% DNA sequence similarity to Bacillus cereus strain HBUAS66958. The three isolates can be combined as a biological control agent of the nematode because they have different targets of nematode life stages. However, a repeated pot assay is necessary to confirm their efficacy prior to field tests.