Rhizobial adhesives enhance nodule formation in sunn hemp

Inoculation of legume seed with rhizobacteria before planting is an efficient and convenient way of introducing effective rhizobacteria to soil vicinity of legume root and ensuring nitrogen fixation in cover cropped field. However, there are still challenges in identifying the proper seed coating technique to ensure microbial survival in adverse environmental conditions and maintaining the symbiotic relation with plants. The objectives of this study are firstly, to analyze the effectiveness of different sticking agents aiding inoculation of Bradyrhizobium japonicum L. in sunn hemp seeds to enhance root nodule formation. Secondly, to observe nodulation pattern over time as affected by the treatment and lastly to check if there is significant difference between main root and lateral root nodulation pattern due to the treatments. Two similar field studies were conducted in fall 2019 and summer 2020 using four sticking agents: water, peanut oil, 10% jaggery solution, and 40% gum arabic solution. The fall study showed no significant differences among total nodules across treatments, but percentage of active nodules was highest in the oil treatment and lowest in the water treatment. In the summer study, significantly higher total nodules were seen in the jaggery treatment and the lowest was in water treatment again, however, there were no differences in percentage of total active nodules across treatments. Interestingly, the trend across weeks showed gum arabic treatment exhibiting higher main root nodulation and jaggery treatment exhibiting higher lateral root nodulation. Overall, water as an adhesive was less effective in aiding nodulation compared to other treatments. Peanut oil and jaggery showed better performance as adhesives aiding active nodulation and could be more effective than gum arabic or water.