Influence of Bradyrhizobium japonicum and Azospirillum strains on activity of antioxidant enzymes in soybean (Glycine max L.) under salt stress condition

The issue of antioxidant enzymes has much attention in saline soils in soybean [Glycine max (L.) Merr.] because salt stress is often limited by Azospirillum strains. In this work, enhanced activity of SOD (Superoxide dismutase) and GPX (Glutathione peroxidase) by interaction of Bradyrhizobium japonicum x Azospirillum: lipoferum (I-1) and Bradyrhizobium japonicum x Azospirillum irakiens (I-2) was investigated as strategies for improved yield of soybean at high rates of NaCl in a greenhouse study. Seedlings were treated by 0, 800,1600 and 2400 mg of NaCl/kg of soil. The effects of I-1 and I-2 on activity of SOD and GPX, grain yield, seeds/pod and seed weight were examined during the 2010 soybean growing season. The experimental design was factorial based on a completely randomized design (CRD) at 7.5 kg rate plastic pots. The results showed that I-1 was more effective on activity of antioxidant enzymes than I-2 at high concentration of NaCl (2400 mg of NaCl/kg of soil). The values of SOD on average in I-2, 20.4 to 14.2% in I-1, 31.3 to 23.6% and 21.4 to 12.3% (I-2) and 25.8 to 16.6% (I-1) for GPX, higher than control treatments, at 800-2400 mg of NaCl/kg soil, respectively. In comparison, in I-1 and I-2 the yield was 37.6 to 28.9% and 31.4 to 23.7% higher than control treatments at 1600 and 2400 mg of NaCl per kg soil, respectively. However, these effects of I-1 and I-2 on antioxidant enzymes could create high yield in response to the damages of NaCl.