Effect of Gluconacetobacter diazotrophicus on Sweet Sorghum (Sorghum bicolor) in Tropical Semi-arid Soil

Abstract

Gluconacetobacter diazotrophicus, an endophytic diazotroph, has been isolated from sugar-rich plants. This organism excretes part of fixed nitrogen in medium. An investigation was undertaken to isolate and evaluate strains of G. diazotrophicus on sweet sorghum (Sorghum bicolor (L.) Moench). Two strains of G. diazotrophicus isolated from endorhizosphere of sweet sorghum (Acd1 and Acd2) were tested for their plant growth potential and nitrogen-fixing ability along with a reference strain obtained from Brazil (Pal3) under green house and field conditions with sweet sorghum cultivar PC 121 in the presence of fertilizer nitrogen (20 and 40 kg N ha−1) applied in the form of isotopically labelled ammonium sulphate [(15NH4)2SO4]. Results indicated that the strains Acd1, Acd2 and Pal3 at 30 and 60 days of plant age increased all the parameters of plant growth over uninoculated control. The performance of the reference strain, Pal3 was superior to Acd1 and Acd2 strains. The bacterial population in the endorhizosphere of the host was higher in inoculated treatments than the controls. It was found that the %N fixed at 30 and 60 days of plant growth was ranging between 0.14 and 1.0 with the use of [(15NH4)2SO4] under greenhouse conditions. In a field experiment, inoculation of G. diazotrophicus (Acd1, Acd2 and Pal3) gave differential response in all plant growth and yield parameters. Strain Pal3 at a nitrogen level of 40 kg N ha−1 recorded the highest straw and grain yield.