Isolation and functional analysis of indigenous Rhizobium spp. from common bean root nodules
TL;DR
Physico-chemical characteristics of soil samples collected from 27 sites situated at different altitudes, grow common bean plants in pots filled with the col - lected soils, and subsequently isolate and characterize indigenous Rhizobium strains from common bean nodules are determined.
Abstract
In the Himalayan region, the identification and isolation of native rhizobia strains for promoting symbiotic nitrogen (N) fixation in common beans have remained unexplored owing to the rough terrain of the region. To bridge the research gaps, this research was designed to determine physico-chemical characteristics of soil samples collected from 27 sites situated at different altitudes (707–2134 m), grow common bean plants in pots filled with the col - lected soils, and subsequently isolate and characterize indigenous Rhizobium strains from common bean nodules. The bacterial populations were assessed using the most probable number (MPN) technique, which ranged from 1.0 × 10⁶–8.0 × 10⁵ cells per gram of soil. Out of 27 isolates tested for biochemical traits, twelve isolates exhibited N fixation potential, 24 isolates were positive for indole-3-acetic acid, and 8 isolates displayed zinc mobilization po - tential. Moreover, 23 and 21 isolates were positive for combined carbon medium source (CCM) and acid production, respectively, while 6 bacterial isolates were found capable of producing alkali. Interestingly, catalase activity was exhibited by 22 isolates, and only 4 isolates effectively solubilized the insoluble phosphate, indicating the significant need to inoculate common beans for boosting grain yield and nutritional value. Thereafter, common bean plants sown in collected soils under a controlled environment revealed that the shoot length varied from 28.6 cm to 48.5 cm, while root length ranged from 6.85 to 22.4 cm. Similarly, the weight of fresh and dry shoots ranged between 4.59–11.5 g and 1.45–4.69 g plant -1 , respectively, while the fresh and dry weight of roots varied between 0.57–1.60 g and 0.27–0.93 g per plant. For developing biofertilizer, isolates (BR3, BR10, BR18, BR20, BR25, BR30, and BR31) may be recommended for high salt tolerance, while BR1, BR8, BR10, BR17, and BR20 stand out in terms of tolerance to varying pH levels owing to superior genetics and better physiological and ecological adaptations.