Alleviation of Salt Stress in Legumes by Co-inoculation with Pseudomonas and Rhizobium

Numerous studies have shown that soil salinity decreases nodulation and dramatically reduces N2 fixation and nitrogenase activity of nodulated legumes. Thus, the development of salt-tolerant symbioses is an absolute necessity to enable cultivation of leguminous crops in salt-affected soils. Dual inoculation of legumes with plant growth-promoting rhizobacteria (PGPR) and rhizobia has been reported to increase the number of nodules compared to those formed by a rhizobial strain alone. The production of IAA by Pseudomonas strains represents a beneficial mechanism that promoted enlargement of root system and thereby further enhanced nutrient uptake, nodulation, and shoot growth of leguminous plants. When PGPR are able to alleviate salt stress experienced by the plant, more nodules might develop into nitrogen-fixing ones, thereby enabling the plant to obtain part of its nitrogen from the atmosphere. Co-inoculation techniques could be a new approach to increase the salt tolerance and yield of legumes used for the food and green manure production in salt-affected soils, providing supply of biologically fixed N at low cost.