Effects of 2,4-D and Azospirillum brasilense on nitrogen fixation, photosynthesis and grain yield in wheat

The effects of 2,4-D with or without Azospirillum brasilense (Sp7) on nodulation of wheat (cv HD2428) have been investigated under hydroponical conditions. In the nutrient medium, varying concentrations of N and 2,4-D were used for growing wheat seedlings. N free Hoagland solution along with 2,4-D (0.5 ppm) was found to be the best concentration for nodulation and growth of the seedlings. The nitrogenase activity (acetylene reduction assay) was relatively higher in plants treated with 2,4D and Azospirillum than with Azospirillum alone. This seemed to be due to the formation of nodule like structure serving as niche for azospirilla to protect it from oxygen. These results confirmed the nitrogenase activity of Azospirillum brasilense in association with the 2,4-D induced nodules of wheat. Plants inoculated with Azospirillum either alone or with 2,4-D were transplanted into pots. The photosynthetic rate, chlorophyll content, NRA, grain yield and N content were found to be higher in inoculated plants. The translocation of current photosynthates (C-14 sucrose studies) towards roots was higher in these treatments. Thus the growth of Azospirillum and nodule formation depend on availability of current photosynthates of host plants.