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

Ahmad Ahmad,Zahid Mumtaz Zahid Mumtaz,Naseer Naseer,Hussain Hussain,Hilger Hilger,Minggang Minggang,Mustafa Mustafa,Ahmad Zahir Ahmad Zahir

doi:10.3390/agronomy9100621

Abstract

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.

Highlights

Chickpea (Cicer arietinum L.) is an important legume crop and is consumed all over the world as a source of protein, carbohydrate, fiber, oil, ash, minerals, vitamins, amino acids and unsaturated fatty acids [1]
More than one hundred non-rhizobial endophytic isolates were isolated from nodules of chickpea and nineteen of these were authenticated as true endophytes by observing their presence in root nodules and induction of nodulation in chickpea
Endophytic Paenibacillus strains isolated from root nodules successfully formed a symbiotic association with chickpea, which was a novel finding

Summary

Introduction

Chickpea (Cicer arietinum L.) is an important legume crop and is consumed all over the world as a source of protein, carbohydrate, fiber, oil, ash, minerals, vitamins, amino acids and unsaturated fatty acids [1]. Chickpea forms a symbiotic relationship with rhizobia that support biological nitrogen fixation (BNF) in root nodules. Rhizobia were thought to be the only nitrogen-fixing inhabitants of legume nodules. Non-rhizobial bacteria were detected within legume nodules revealing the existence of a phytomicrobiota where the interaction among the individuals is complex and affects the behaviour and fitness of the host plant [4]. These non-rhizobial bacteria are involved in BNF through inducing nitrogen fixing nodules on roots of host legume [5]

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