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.
Root-knot nematodes (RKN) cause considerable economic losses to kiwifruit production annually. Screening of resistant cultivars has been one of the long-standing methods to manage root-knot nematodes. Here, the reaction of the four most common commercial cultivars of kiwifruit, namely, Actinidia chinensis var. deliciosa cv. Hayward, A. chinensis var. deliciosa cv. Abbott, A. chinensis var. deliciosa cv. Bruno, and A. chinensis var. chinensis cv. Haegeum (commonly known as ‘Golden’ kiwifruit) to infection by the RKN, Meloidogyne incognita, was evaluated. Among examined cultivars ‘Golden’ was the most susceptible, having on average 52.8 galls, 56.1 egg masses per gram of root, and 642 J2 population per 200 gram of soil. ‘Bruno’ showed the highest resistance, with 3.3 galls, 4.1 egg masses per gram of root, and 79 J2 in 200 g of soil. Then, two potential biological control agents, namely Priestia megaterium 31.en and Agrobacterium tumefaciens 19.en were used on ‘Hayward’ seedlings against M. incognita and showed a significant reduction in the number of galls and egg masses on roots, juvenile population in the soil, and increased the growth parameters of the plants compared to non-treated seedlings. We demonstrated that integrated management using resistant cultivars and biological control can provide a safe and economic method to control RKN, and these resistant cultivars can be used in breeding programs.
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