Alleviation of Salinity Stress Effects in Forage Cowpea (Vigna unguiculata L.) by Bradyrhizobium sp. Inoculation

Abstract

To investigate salt stress and inoculation effects on nodulation and growth of forage cowpea (Vigna unguiculata cv. Baladi), experiments were conducted under laboratory, greenhouse and field conditions. Six isolates were tested for salt tolerance by culturing in liquid medium supplemented with 5, 10, 15, 20, 25 and 30 g L-1 NaCl and for their nodulation and N2-fixation abilities under different soil  salinity (1.87, 3.16, 5.88, 9.12 and 12.14 dS m-1), were evaluated, followed by application of  single and dual inoculation with the two selected halo-tolerant isolates on the growth dynamics in salt-affected soils (9.12 dS m-1), under normal and saline irrigation water during 2016 and 2017 seasons. In liquid medium supplemented with 30 g L-1 NaCl, results showed that isolate of SARS-Rh5 was the most tolerant to grow compared to the others. In respect to the inoculation, the highest values of plant height (20.26 and 20.73 cm plant-1), dry weight of plant (1.08 and 1.11 g plant-1), dry weight of nodules (0.056 and 0.056 g plant-1), and nitrogen content (22.26 and 23.82 mg plant-1), were recorded by SARS-Rh3 and SARS-Rh5 isolates compared to other isolates and control, respectively.  In a field trial, a highly significant increase caused by dual inoculation with SARS-Rh3 + SARS-Rh5 (T4), in nodulation, growth and yield compared to single inoculation treatments and control. Also, an increase of 30% in K+ content and 45% in K+/Na+ ratio but reached to the reduction of 10% in Na+ content were noticed during the two growing seasons. So that, the inoculation of cowpea plants grown under soil salinity conditions with tolerant Bradyrhizobiumis very urgent to help the plant to circumvent the unfavourable conditions.