Selection of thermotolerant bradyrhizobial strains for nodulation of soybean (Glycine max L.) in semi-arid regions of Iran

Abstract

Nodulation of soybeans grown in semi-arid region of southern parts of Iran is poor due to high air and soil temperatures. Here we identified thermotolerant isolates of soybean bradyrhizobia and evaluated the nitrogen fixation efficiency of the isolates under heat stress conditions in greenhouse and field experiments. The ability of fifty-six bradyrhizobial isolates to grow on solid or in liquid yeast extract mannitol medium at 38 and 41°C was evaluated. We identified 19 isolates, which were able to grow at 38°C and 10 isolates able to grow at 41°C. Greenhouse experiments were carried out at 28 and 38°C to study the nitrogen-fixing capacity of the isolates under optimal and high temperature conditions. Ten isolates had a symbiotic index of effectiveness of 80% or greater compared with nitrogen-fertilized treatments in greenhouse experiments at 28°C. Some thermotolerant isolates demonstrated good nitrogen-fixing performance at 38°C. Eight isolates were selected for use in a field trial in the natural high temperature environment of the Dezful region in Iran. Our results demonstrate that geographical origin can have a great influence on the successful selection of thermotolerant bradyrhizobia. Our thermotolerant isolates were mainly obtained from high-temperature regions, and improved shoot dry matter, nitrogen-uptake and seed yield of the plants.

Effect of Native Soybean Rhizobia and AM Fungi in the Improvement of Nodulation, Growth, Soil Enzymes and Physiological Status of Soybean Under Microcosm Conditions

“…Similarly, inoculation of AM fungi and rhizobia significantly improved N and P uptake in soybean. Present findings are in agreement with the work of Rahmani et al [24], where they showed that effective and thermotolerant isolates were able to fix nitrogen and increase soybean dry weight and nitrogen content of the shoots as well as in the seed yield. Previous studies carried out proposed that nitrogen fixation in soybean are sensitive to high temperatures [13].…”

The biodiversity of beneficial microbe-host mutualism: the case of rhizobia

“…pH, temperature and land use also influencing the outcome (Botha et al, 2004;Obaton et 367 al., 2002;Rahmani et al, 2009;Sadowsky, 2000). 368…”

Tolerance of Mesorhizobium type strains to different environmental stresses

“…The maximum growth temperature range for rhizobia from tropical grain legumes has been described between 32 and 47°C (Hungria and Vargas 2000). Studies with soybean bradyrhizobia showed that strains endurance to high temperatures in culture medium correlates with their symbiotic performance under heat stress (Rahmani et al 2009). …”