Growth-Promoting Characteristics of Fungal and Bacterial Endophytes Isolated from a Drought-Tolerant Mint Species Endostemon obtusifolius (E. Mey. ex Benth.) N. E. Br

Abstract

Endophytes are primarily endosymbiotic bacteria and fungi that colonize the interior tissues of their host plant. They enhance the host plant’s growth and attenuate adverse effects of biological stress. Endophytic species of many indigenous plants are an untapped resource of plant growth-promoting microorganisms that can mitigate abiotic stress effects. Thus, this study aimed to isolate endophytes from the roots and leaves of the medicinal plant Endostemon obtusifolius to evaluate their in vitro growth-promoting capacities and drought tolerance and to characterize the most promising species. Twenty-six endophytes (fourteen bacteria and twelve fungi) were isolated and cultured from the roots and leaves of E. obtusifolius. All 26 endophytes produced flavonoids, and 14 strains produced phenolic compounds. Of the 11 strains that displayed good free radical scavenging capability (low IC50) in the 1-1-diphenyl-1-picryhydrazyl radical scavenging assay, only three strains could not survive the highest drought stress treatment (40% polyethylene glycol). These 11 strains were all positive for ammonia and siderophore production and only one strain failed to produce hydrogen cyanide and solubilize phosphate. Seven isolates showed aminocyclopropane-1-carboxylate deaminase activity and differentially synthesized indole-3-acetic acid. Using molecular tools, two promising symbiotic, drought stress tolerant, and plant growth-enhancing endophytic species (EORB-2 and EOLF-5) were identified as Paenibacillus polymyxa and Fusarium oxysporum. The results of this study demonstrate that P. polymyxa and F. oxysporum should be further investigated for their drought stress mitigation and plant growth enhancement effects as they have the potential to be developed for use in sustainable agricultural practices.

Fungal endophytes from saline-adapted shrubs induce salinity stress tolerance in tomato seedlings

“…Our experiment used four fungal endophytes that were selected based on their abilities to produce the exoenzymes amylase, protease and cellulases and to solubilize inorganic phosphorus. Of the 60 fungal isolates obtained, 62% solubilized inorganic phosphate, a finding that agrees with those of Ogbe et al ( 2023 ). Phosphorus is the second most important plant nutrient after nitrogen (Radhakrishnan et al 2015 ).…”

“…They can also produce mycotoxins that are passed on to animals when they feed on contaminated plants; and they can act as pathogens to humans (Ji et al 2019 , Srinivas et al 2019 ). However, Fusarium endophytes in plants have been shown to lose their pathogenicity under stress conditions, and thus they become beneficial to the plant by inducing resistance to stress and enhancing growth (Pappas et al 2018 , Ogbe et al 2023 ). This characteristic can be a key reason why plants symbiotically associate with Fusarium species.…”

Deciphering the mechanisms, hormonal signaling, and potential applications of endophytic microbes to mediate stress tolerance in medicinal plants

“…The higher level of putrescine and free cellular spermidine is positively linked with water stress ( Sen et al., 2018 ). Recently, Endostemon obtusifolius plant inoculated with Paenibacillus polymyxa and Fusarium oxysporum showed enhanced drought tolerance ( Ogbe et al., 2023 ). In other studies Streptomyces dioscori SF1 strain enhanced drought, salinity and phytopathogen resistance in Glycyrrhiza uralensis via the production of ammonia, IAA, enzyme activities, potassium solubilization, nitrogen fixation and Sphingomonas paucimobilis ZJSH1 strain ameliorate drought, salt, and heavy metal toxicity in Dendrobium officinale plants ( Li X. et al., 2023 ; Li J. et al., 2023 ).…”

Cultivable Endophyte Resources in Medicinal Plants and Effects on Hosts

“…Bacteria, as the largest group of plant endophytes, have been isolated from many kinds of medicinal plants and widely studied due to their biocontrol functions [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. By reviewing the recent literature on most of the endophytic bacteria of medicinal plants including Bacillus sp., Pseudomonas sp., Enterobacter sp., Agrobacterium sp., etc., and a large number of endophytic bacteria in the roots, stems, and leaves, we collated some of the relevant data of the isolated endophytic bacteria in Table 1 .…”

“…SX19 and Colletotrichum gloeosporioids showed strong inhibitory effects on five pathogens. Ogbe et al [ 30 ] isolated a total of 11 endophytic fungi from the roots and leaves of a drought tolerant mint species Endostemon obtusifolius . Similarly, five endophytic fungi were isolated from the leaf segments of wild Dendrobium nobile and identified as Colletotrichum tropicicola , Fusarium keratoplasticum , Fusarium oxysporum , Fusarium solani , and Trichoderma longibrachiatum [ 44 ].…”