VARIABILITY IN STRESS TOLERANCE AND POTENTIAL OF ENDOPHYTIC BACTERIA TO IMPROVE CHICKPEA GROWTH UNDER WATER LIMITED CONDITIONS

The production of agricultural crops is reducing due to the prevalence of drought like situations in the world (Fahad et al., 2017). Inoculation with plant growth promoting bacteria has been devised as a beneficial strategy for improving the fitness of crop plants especially under harsh environmental conditions. Bacteria in the rhizosphere face various conditions to ensure their survival through competition with indigenous microflora for nutrition and harsh environmental conditions before playing their role as plant growth promoter (Martinez et al., 2010). Predation by protozoans aggravates the problem of inoculums failure in field conditions by limiting survival of plant growth promoting bacteria (PGPB) in the rhizosphere. Ultimately, the role of rhizosphere bacteria as plant growth promoter is verily dependent on their capability to survive and flourish under hostile environments (Rivera et al., 2008). While in distressed conditions some bacteria become advantageous due to their capability to enter, survive and express their plant beneficial traits inside the plant tissues. They live for the entire or part of their life cycle inside the plant without being pathogenic and are termed as endophytes (Hardoim et al., 2008). Bacteria as endophytes escape/avoid the competition with indigenous microflora for space and resources and adverse soil conditions. They get incubation in plant tissue at optimal temperature, space and nutrition (Beattie, 2007; Rosenblueth and Martinez-Romero, 2006). Endophytic bacteria are almost similar in their plant growth promoting attributes to rhizobacteria. They increase plant vigor and induce tolerance/resistance against biotic/abiotic stresses like drought (Hallmann et al., 1997; Naveed et al., 2014) and modulate the plant stress response (Dudeja and Giri, 2014). The plant growth promoting mechanisms by endophytic bacteria include the production of phytohormones, nitrogen fixation, siderophores production and production of antimicrobial compounds against plant pathogens (Hallmann et al.,1997; Rosenblueth and MartinezRomero, 2006; Mitter et al., 2013). It has been observed that endophytic bacteria improve plant growth, biomass, root growth and protect the plants from drought by supplying growth regulators, osmolytes and nutrients (Kavamura et al., 2013; Egamberdieva, 2017). Using endophytes on behalf of their advantages to avoid harsh soil environments is a new trend in sustainable agriculture. Though, researchers have tried different endophytes to improve growth, physiology, yield and abiotic stress tolerance in cereals. However, endophytes in legumes other than Pak. J. Agri. Sci., Vol. 55(3), 531-539; 2018 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/18.6654 http://www.pakjas.com.pk