Rhizobial inoculation improves seedling emergence, nutrient uptake and growth of cotton

Experiments were conducted to determine the growth promoting activities of various rhizobia in cotton (Gossypium hirsutum L.) under growth room conditions. Seeds of 4 cotton cultivars were inoculated with 4-indole-3-acetic acid producing selected (Brady) rhizobium strains and Azotobacter plant growth promoting rhizobacteria strains, included as a positive control. Growth responses to inoculation exhibited bacterial strain-cotton cultivar specificity and also included increase in rate of seedling emergence by 3-9%. Shoot dry weight, biomass and N uptake were increased by 48, 75 and 57%, respectively, due to inoculation with both the Rhizobium leguminosarum bv. trifolii E11 and Azotobacter sp. S8, whereas, strain E11 also increased root dry weight, root length and area by 248, 332 and 283%, respectively. K+ and Ca2+ uptake was also increased by 2-21% and 9-14%, respectively, due to rhizobial inoculation. The results also showed that ( Brady) rhizobium strains promoted cotton growth through efficient nutrient uptake, which was mainly related to increased root growth due to the effect of IAA produced by these strains. However, growth promotion by Azotobacter sp. S8, in addition to 4-indole-3-acetic acid production, might also involve biological N-2 fixation by this rhizobacterial strain at some stage during its growth.