Appraising Endophyte–Plant Symbiosis for Improved Growth, Nodulation, Nitrogen Fixation and Abiotic Stress Tolerance: An Experimental Investigation with Chickpea (Cicer arietinum L.)

Chickpea is an important leguminous crop that improves soil fertility through atmospheric nitrogen fixation with the help of rhizobia present in nodules. Non-rhizobia endophytes are also capable of inducing nodulation and nitrogen fixation in leguminous crops. The aim of the current study was to isolate, characterize and identify the non-rhizobia endophytic bacterial strains from root nodules of chickpea. For this purpose, more than one hundred isolates were isolated from chickpea root nodules under aseptic conditions and were confirmed as endophytes through re-isolating them from root nodules of chickpea after their inoculation. Nineteen confirmed endophytic bacterial strains revealed significant production of indole acetic acid (IAA) both in presence and absence of L-tryptophan and showed their ability to grow under salt, pH and heavy metal stresses. These strains were evaluated for in vitro plant growth promoting (PGP) traits and results revealed that seven strains showed solubilization of P and colloidal chitin along with possessing catalase, oxidase, urease and chitinase activities. Seven P-solubilizing strains were further evaluated in a jar trial to explore their potential for promoting plant growth and induction of nodulation in chickpea roots. Two endophytic strains identified as Paenibacillus polymyxa ANM59 and Paenibacillus sp. ANM76 through partial sequencing of the 16S rRNA gene showed the maximum potential during in vitro PGP activities and improved plant growth and nodulation in chickpea under the jar trial. Use of these endophytic strains as a potential biofertilizer can help to reduce the dependence on chemical fertilizers while improving crop growth and soil health simultaneously.