Beneficial effects and molecular diversity of endophytic bacteria in legume and nonlegumes

Abstract

Endophytes colonize the plant inner tissues, commonly coming from the soil. Endophytes could be considered of two types, one having plant growth-promoting activity, while another type having the ability to fix nitrogen. Endophytic bacteria can stimulate plant growth directly through production of phytohormones and volatiles, enhance nutrient acquisition, and suppress stress-induced ethylene synthesis. Bacterial endophytes protect against disease, against abiotic stresses of salinity and heavy metals. Pathogenic, symbiotic nitrogen fi xers and mycorrhiza coordinate sequential expression of plant or microbial genes. But in both types of endophytic association, partial interactions, signaling pathways, coordination, and gene expression of host and bacteria are known. To obtain nitrogen- fi xing cereals, now emphasis has been shifted from rhizobia to actinorhizal symbiosis based on the recent studies on model legumes. Endophytic bacteria have been found in almost every plant studied. All plants may harbor one or more number of bacteria of genera mainly Bacillus, Paracoccus, Sphingomonas, Inquilinus, Pseudomonas, Serratia, Mycobacterium, Nocardia, Brevibacillus, Staphylococcus, Lysinibacillus, Bosea, Rhodopseudomonas, Phyllobacterium, Ochrobactrum, Starkeya, Agromyces, Ornithinicoccus, Actinobacterium, Paenibacillus, Methylobacterium, Pedobacter, Aerococcus, Stenotro-phomonas, Streptomyces, Dyella, and others. Most of the endophytic isolates upon inoculation in different agricultural crops signifi cantly increased plant growth under greenhouse conditions. This plant growth promotion is the result of many different factors that can act directly or indirectly. Effi cacy of two endophytic bacterial strains Bacillus subtilis and B. licheniformis under fi eld conditions showed that an increase up to 22.5 % in grain yield of chickpea was observed with Bacillus subtilis inoculation. However, inoculation with all the recommended biofertilizers – Mesorhizobium, PSB and PGPR – could increase up to 14.4 % grain yield in chickpea.