Synergistic Plant-Microbe Interactions between Endophytic Actinobacteria and Their Role in Plant Growth Promotion and Biological Control of Cotton under Salt Stress

Abstract

Bacterial endophytes are well-acknowledged inoculants to promote plant growth and enhance their resistance toward various pathogens and environmental stresses. In the present study, 71 endophytic strains associated with the medicinal plant Thymus roseus were screened for their plant growth promotion (PGP), and the applicability of potent strains as bioinoculant has been evaluated. Regarding PGP traits, the percentage of strains were positive for the siderophore production (84%), auxin synthesis (69%), diazotrophs (76%), phosphate solubilization (79%), and production of lytic enzymes (i.e., cellulase (64%), lipase (62%), protease (61%), chitinase (34%), and displayed antagonistic activity against Verticillium dahliae (74%) in vitro. The inoculation of strain XIEG05 and XIEG12 enhanced plant tolerance to salt stress significantly (p < 0.05) through the promotion of shoot, root development, and reduced the activities of antioxidant enzymes (SOD, POD, and CAT), compared with uninoculated controls in vivo. Furthermore, inoculation of strain XIEG57 was capable of reducing cotton disease incidence (DI) symptoms caused by V. dahliae at all tested salt concentrations. The GC-MS analysis showed that many compounds are known to have antimicrobial and antifungal activity. Our findings provide valuable information for applying strains XIEG05 and XIEG12 as bioinoculant fertilizers and biological control agent of cotton under saline soil conditions.

Inoculation with Actinobacteria spp. Isolated from a Hyper-Arid Environment Enhances Tolerance to Salinity in Lettuce Plants (Lactuca sativa L.)

“…Numerous reports are available on their potential as agents for promoting plant growth [ 40 , 41 ]. Our results are in concordance with Mohamad et al (2022), who reported a significant increase in the total fresh weight of cotton plants under different salt conditions when the plants were inoculated with actinobacterial strains Streptomyces luteus XIEG05 and Nocardiopsis dassonvillei XIEG12 [ 42 ]. In the same way, the Streptomyces sp.…”

Optimisation of indole acetic acid production by Neopestalotiopsis aotearoa endophyte isolated from Thymus vulgaris and its impact on seed germination of Ocimum basilicum

“…On the other hand, fungi release phytohormones, volatile chemicals, and siderophores, which can either indirectly or directly promote plant development by making their host more nutrient-available [ 48 ]. Several endophytic bacteria with valuable metabolites for agriculture and biotechnology are present in different medicinal plants [ 49 , 50 ].…”

Drought and salt stress mitigation in crop plants using stress-tolerant auxin-producing endophytic bacteria: a futuristic approach towards sustainable agriculture

“…(2022) three endophytic bacteria were screened from the medicinal plant, Thymys roseus , demonstrating the capability to produce auxin and tolerate up to 200 µM NaCl stress. Upon inoculation of these bacteria into cotton plants, Streptomyces atrovirens exhibited the greatest increase in root length and weight compared to the control, while Alloactinosynne album caused the maximum increase in shoot length and weight ( Mohamad et al., 2022 ).…”

“…Furthermore, their use can lead to unregulated or irregular plant growth tendencies, such as epinasty ( Bhojwani, 2012 ; Keswani et al., 2020 ) Another alternative approach involves the contribution of plant-associated beneficial microorganisms, which have been reported to augment auxin levels in plants ( Arshad and Frankenberger, 1991 ; Nassar et al., 2005 ; Tsavkelova et al., 2007 ; Shi et al., 2009 ; Keswani et al., 2020 ; Iqbal et al., 2023 ). Endophytic bacteria have been documented to promote plant growth in various crops including rice ( Walitang et al., 2017 ), wheat ( Yandigeri et al., 2012 ; Patel and Archana, 2017 ), maize ( Riggs et al., 2001 ), potato ( Nowak et al, 1995 ; Pavlo et al., 2011 ), cucumber ( El-Tarabily et al., 2009 ; Shaalan et al., 2021 ), cotton ( Bashan et al., 1989 ; Mohamad et al., 2022 ; Verma et al., 2022 ), tomato ( Pillay and Nowak, 1997 ; Agarwal et al., 2020 ).…”