Isolation and Characterization of Endophytic Fungi From Halophytes for the Synthesis of Indole Acetic Acid, Stress Tolerance and Plant Growth Promoting Properties

Abstract

Soil contamination is a serious environmental concern, cost effective and efficient means are needed to address this problem worldwide. Soil microorganisms have enormous diversity; in their symbiotic association with higher plants they help thrive their hosts in soils that are affected by heavy metals or salts. Exploration of such proficient microbial diversity can help crop plants to mitigate the negative impacts of soil stresses. During the current study, 12 different strains of endophytic fungi were isolated from halophytic plants Solanum surattense, Chenopodium album and Zizyphus nummularia aiming to study the plant growth promoting potential of endophytic fungi on wheat plants cultivated on saline and heavy metals (Ni, Cd, Cu, Zn, and Pb) affected soils. In cultural filtrate assays, two strains CGF-1 and CGF-11 produced maximum IAA and conferred fitness benefits under both stresses and had antimicrobial as well as antioxidant potential. Strains were characterised on morphological as well as diversity of the ITS regions of the 18s rDNA as Penicillium ruqueforti (CGF-1) and Trichoderma reesei (CGF-11). P. roqueforti induced resistance in wheat plants grown on heavy metal contaminated soil and T. reesei was effective under saline conditions, indicating to the potential of both endophytes in phytostablization under stress conditions. Application of P. roqueforti restricted the transfer of heavy metals from soil to the plants by secreting indole acetic acid (IAA). Likewise, T. reesei rescued wheat plant from salinity by secreting siderophores and 1-aminocyclopropane-1-carboxylic acid (ACC). Moreover, P. roqueforti and T. reesei inoculated wheat plants had higher plant growth, nutrient uptake and low concentrations of heavy metals and salts in shoots and roots. Similarly, inoculated wheat plants had higher chlorophyll a, b and carotenoids contend and displayed reduced glutathione (GSH), ascorbate, peroxidase, catalase activity. The fungal inoculated wheat seedlings had higher IAA, GA, Ca, K, phenol, sugar and proline, while lower ABA, H2O2 electrical conductivity, malondialdehyde (MDA), Na and Cl contents to combat stresses compared to the control. The results revealed that P. roqueforti and T. reesei inoculation could establish a symbiotic relationship with host plants, and help host wheat plants to flourish in soils that are affected by heavy metals or salinity. The ethyl acetate extracts of both strains was tested for antimicrobial activity, both P. roqueforti and T. reesei had broad-spectrum activity against phyto-pathogenic bacteria (Xanthomonas oryzae, Pseudomonas syringae, Agrobacterium tumefaciens and Ralstonia solanacearum). Further, the ethyl acetate extracts P. roqueforti and T. reesei revealed presence of alkaloids, flavonoids, phenols, steroids and tannins. HPLC analyses also confirmed presence ferulic acid, cinnamic acid, quercetine and rutine in the ethyl acetate extracts. Our results have wider implications for sustainable agriculture and P. roqueforti as well as T. reesei could protect wheat plants and may play an active role in addressing both biotic and abiotic stresses of future.