Alleviating salt stress on soybean (Glycine max (L.) Merr.) – Bradyrhizobium japonicum symbiosis, using signal molecule genistein

For the onset of symbiosis process between soybean (Glycine max (L.) Merr.) and Bradyrhizobium japonicum, signals should be exchanged. Salinity has inhibitory effects on the symbiosis between the two partners. Hence, a greenhouse experiment was planned to: (1) determine the stressful effects of salinity on soybean and B. japonicum symbiosis, hypothesizing that they can inhibit the signal exchange process between the two partners, and (2) determine if the addition of genistein (a nod gene inducer) to B. japonicum (strain 532C) inocula could overcome the stressful effects of salinity on the Bradyrhizobium – soybean symbiosis. Three levels of salinity (control, 36 and 61 mmolar or 3.6 and 6.1 mmhos/cm) and three levels of genistein (0, 5 and 20 μM) were combined in a factorial fashion in four replicates. Soybean plants were harvested at three different times including 20, 40 and 60 days after inoculation (DAI). Genistein enhanced soybean nodulation and growth, and such effects became greater with time under high salinity levels. For example, at 60 DAI the enhancing effects of genistein on the symbiosis process in soybean was more pronounced at the highest level of salinity. The significant interaction effect between genistein 5 μM and salinity 61 mmolar may reveal the direct role of genistein 5 μM in overcoming the stressful effects of salinity on the symbiosis between B. japonicum and soybean, and hence, plant growth. This novel finding may be very useful to increase soybean yields in salty croplands.