Testing Local Isolates of Rhizobium leguminosarum at Different Salinity Levels and Their Potential Use as Biofertilizer

Abstract

Rhizobium bacteria are among the most important beneficial soil microbes because they contribute to atmospheric nitrogen fixation and live symbiotically with leguminous plants. Nitrogen is one of the essential nutrients for plants, present in the atmosphere at about 79%, but plants cannot directly utilize it from the air. Its availability depends on soil type. The aim of this study was to test the ability of isolates to grow in environments with different salt concentrations, select the best isolates for salt tolerance, and evaluate their potential use as biofertilizers after further studies. Six isolates of R. leguminosarum were obtained from root nodules of Vicia faba (broad bean) collected from different regions in western Libya: Bir Al-Touta (RL 01), Souq Al-Sabt (RL 02), Qasr Bin Ghashir (RL 03), Ain Zara (RL 04), Msallata (RL 05), and Al-Khums (RL 06). Some chemical tests were performed to confirm their identity. In this research, the effect of several salinity concentrations on Rhizobium growth was studied using nutrient media with different sodium chloride levels (0 ppm, 3000 ppm, 6000 ppm, 9000 ppm). Growth efficiency was assessed by culturing the isolated colonies. Results showed that RL 01 colonies were inhibited at all concentrations except the control, while RL 04 colonies were inhibited at 6000 ppm and 9000 ppm. Among the six isolates studied, RL 02, RL 03, and RL 05 were the most tolerant to salinity, whereas RL 06 was the least resistant compared to the others.