In vitro antifungal activity of endophytic bacteria isolated from date palm (Phoenix doctylifera L.) against fungal pathogens causing leaf spot of date palm

Abstract

Background Date palm ((Phoenix doctylifera L.) suffers from several fungal diseases. The endophytic microorganisms present in higher plants generally offer protection to their host plants against invading phytopathogenic fungi and bacteria. In the present study, endophytic bacteria associated with date palm leaves were isolated and their in vitro antagonistic potential against fungal pathogens causing leaf spots in date palm was demonstrated. Results Endophytic bacteria were isolated from date palm leaves of 3 different cultivars viz., Nighal, Khalas and Khinaizi and evaluated for their inhibitory activity against leaf spot pathogens of date palm viz., Fusarium solani, Alternaria sp., Nigrospora sp., Thieloviopsis sp., Curvularia subpapendrofii and Tilletiopsis minor using an in vitro dual culture assay. Of the 24 endophytic bacterial strains tested, the endophytes designated B1, B7, B8 and B9 obtained from cv. Nighal showed inhibitory activities (more than 55% mycelial growth inhibition) against F. solani and Alternaria sp. None of the bacterial endophytes inhibited the growth of other fungal pathogens tested. These antagonistic bacterial strains were identified as Pantoea septica on the basis of 16S rRNA gene sequence analysis. The hyphae of F. solani and Alternaria sp. exhibited morphological abnormalities such as shrinkage and disintegration when grown in the presence of antagonistic bacterial endophytes. The cell-free culture filtrates of the bacterial endophytes caused inhibition of mycelial growth and induced leakage of electrolytes from the mycelia of F. solani and Alternaria sp. This is the first study that describes inhibition of the date palm pathogens F. solani and Alternaria sp. by P. septica. Conclusion Endophytic Pantoea septica strains isolated from date palm leaves inhibited the mycelial growth of F. solani and Alternaria sp. and induced morphological changes in their mycelia. The culture filtrates of these bacterial strains also inhibited the mycelial growth and caused leakage of electrolytes from the mycelia of F. solani and Alternaria sp. These promising bacterial strains can be exploited as biocontrol agents to control F. solani and Alternaria sp.-induced leaf spot diseases of date palm.

Screening of Endophytic Bacteria Isolated from Weed Plant to Biocontrol Stem Rot Disease on Pitaya (Hylocereus undatus)

“…The current study shows that the inoculation of plants with endophytic bacteria with phosphate solubilization (PSB) and IAA production resulted in greater plant growth than un-inoculated plants. These results are consistent with some previous reports, in which the use of PSB enhanced growth, yield, and quality in many crops including walnut, apple, maize, rice, mustard, oil palm, aubergine and chili, soybean, wheat, sugar beet, sugarcane, chickpea, peanut and legumes, and potatoes [36,41]. It is proposed that the antagonistic bacteria in this study produced extracellular metabolites (such as GA) that resulted in the release of soluble phosphate and subsequently up-took by the plant [42].…”

“…These compounds caused leakage of cellular electrolytes from the mycelium of A. alternata resulting in the shrinkage of hyphae. The leakage of electrolytes from fungal membranes has previously been reported as an indicator of cell membrane damage [35,36]. The results of the present study suggest the production of antifungal compounds as one of the possible mechanisms of action of these endophytic bacterial strains on the tested fungal pathogens.…”

Evaluation of the Antifungal Activity of Bacillus amyloliquefaciens and B. velezensis and Characterization of the Bioactive Secondary Metabolites Produced against Plant Pathogenic Fungi

“…Some studies consider bacterial endophytes as potential biocontrol agents for various hazardous fungi [ 6 , 7 ]. Selim et al [ 17 ] and Riera et al [ 49 ] revealed that Streptomyces , Pseudomonas , Bacillus , and Agrobacterium have long been the most important bacteria genera for the production of active antimicrobial substances.…”

“…The biological methods of controlling diseases that affect plants is an eco-friendly alternative, especially applicable when there is pesticide resistance and the need for environmental protection toward sustainable agricultural methods [ 4 , 5 ]. Microbial antagonists have unique properties that inhibit fungal infection growth through direct and indirect processes [ 6 , 7 ]. The direct impact is mainly owing to the biocontrol agent’s antagonistic behavior against the pathogen due to competition, parasitism, antibiosis, and the production of extracellular digestive enzymes.…”

“…The direct impact is mainly owing to the biocontrol agent’s antagonistic behavior against the pathogen due to competition, parasitism, antibiosis, and the production of extracellular digestive enzymes. In contrast, plant defense mechanisms are triggered in response to various pests and diseases, which has an indirect effect [ 7 , 8 , 9 ].…”