Isolation, Identification and Biocontrol Activity of Novel Chitinolytic Bacteria against Meloidogyne incognita Infecting Capsicum annuum L.

In the era of climate change, environmental degradation caused by the unabated and indiscriminate usage of synthetic nematicides, there is urgent demand to develop safe alternatives for management of nematode diseases.  In this respect, this study aimed to isolate, characterize, and evaluate novel chitinolytic rhizobacteria as biocontrol agents against Meloidogyne incognita infecting Capsicum annuum L.  Among seventeen chitinolytic bacterial isolates, which were isolated from nematode suppressive soil, five isolates exhibited high chitinolytic activity. These isolates were identified based on ۱۶S rRNA gene analysis as Chryseobacterium daecheongense (isolate AB۱), Bacillus toyonensis (isolate AB۲), Pseudomonas lini (isolate AB۳), Lactobacillus helveticus (isolate AB۴) and Klebsiella oxytoca (isolate AB۵). In vitro studies revealed that maximum nematode mortality (۱۰۰%) was recorded for isolates AB۳ and AB۵; while maximum egg hatching inhibition (۹۰.۸۶ and ۸۶.۲۷%) in AB۳ and AB۴, respectively. Under field conditions, maximum inhibition in gall formation, female numbers, egg-mass production, developmental stages and final population of juveniles in soil, was recorded for AB۳, AB۴ and AB۵ isolates, respectively. The accumulation of phenolic compounds, peroxidase and polyphenol oxidase in pepper leaves were induced by different bacterial treatment which played a significant role in resistance of the plant to biotic stress. The histological study showed poor formation of regular giant cells in pepper roots treated with chitinolytic bacterial strains. Root transverse section of pepper plants infected with M. incognita and treated with isolates AB۳ and AB۴ showed maximum healthy pattern and less necrotic points compared to the control. In conclusion, this study demonstrated that among the tested bacterial stains, P. lini (AB۳), L. helveticus (AB۴) and K. oxytoca (AB۵) showed high biocontrol prospects against M. incognita and could be introduced and formulated as a promising, affordable and safe bionematicides. Moreover, C. daecheongense (AB۱) was recorded for the first time for its nematicidal activity.

Keywords:

Rhizobacteria , Chitinase , biological control , Meloidogyne incognita , Capsicum annuum L