Isolation and identification of endophytic bacteria associated with kiwifruit and their biocontrol potential against Meloidogyne incognita

Abstract

Background: Root-knot nematodes (RKNs) cause severe losses in kiwifruit-growing regions. The endophytic bacteria could be biological agents for nematodes management. The aim of this study was the isolation and identification of endophytic bacteria from kiwifruit orchards and the evaluation of their antagonistic ability against RKN in greenhouse conditions. Results: In this study, the population of nematode and the bacterial strains were isolated from kiwifruit roots and leaves in the Mazandaran and Guilan provinces of Iran. Molecular experiments were conducted to identify and confirm the bacterial isolates and RKN species. Also, the effects of bacterial isolates on nematode reproduction factors (number of galls, egg masses, and second-stage juveniles, J2) and growth parameters of kiwifruit plants were determined. The RKN was confirmed as Meloidogyne incognita by molecular identification. Also, the endophytic bacteria were identified based on supplementary experiments and molecular analyses. A total of 31 bacterial endophytes were identified to be including 12 genera of Bacillus, Pseudomonas, Staphylococcus, Exiguobacterium, Sphingomonas, Agrobacterium, Variovorax, Pantoea, Microbacterium, Streptomyces, Chryseobacterium, and Chitinophaga. Generally, Bacillus and Pseudomonas were the dominant genera that included 29.03 and 22.58% of total isolated bacteria, respectively. In vitro screening assays, P. ananatis 121.en and P. chlororaphis 54.en displayed considerable antagonistic ability on J2 mortality of M. incognita and were selected for greenhouse surveys. The isolates displayed a significant reduction in the number of galls and egg masses on roots and juvenile’s population in pot soil. Moreover, 121.en and 54.en strains significantly increased growth parameters including root fresh weight and shoot fresh weight than the control kiwifruit seedlings. Conclusions: The bacterial endophytes are safe and have a low risk of managing the RKNs and can be effective microbial bio-fertilizers for improving kiwifruit plant growth under RKNs infections.