Relative potential of rhizobium species to enhance the growth and yield attributes of cotton (Gossypium hirsutum L.)

Legumes compensate mineral fertilizer by fixing nitrogen due to the specialized structures i.e. nodules by Rhizobium species. Literature revealed that legumes fixed nitrogen due to Rhizobium inoculation from 50-300 kg NPK ha-1 year-1. Rhizobium besides nitrogen fixation, solubilized phosphates, produced growth hormones and due to its root colonizing ability improved the growth and yield of non-legumes also and performed as plant growth promoting rhizobacteria (PGPR). Study was conducted to assess the relative efficiency of Rhizobium species for the growth and yield of cotton. Different isolates of five species of Rhizobium species responsible for different nodule formation in legumes were assessed for the auxin biosynthesis potential as IAA equivalents and isolates having higher values for IAA equivalents were used for experimentation. Results revealed that isolates of Rhizobium species improved the growth and physiological parameters of cotton. Higher values were root/shoot length and mass were observed with Rhizobium species of berseem (Br5). Bacterial inoculation with isolate (Br5) produced 60.94, 64.40 g shoot/root mass that is 16.70 and 23.80 % higher than control and percent increase improvements of cotton shoot/root length with Br5 i.e. 18.3, 24.8 % higher than that of control. Higher values of IAA equivalents were observed in root/shoot content of cotton with isolate of Br5. Bacterial inoculation improved the plant height, boll weight, number of bolls plant-1 and seed cotton yield with Br5 inoculation. The chlorophyll content, photosynthetic rate, transpiration rate and photo active radiation were also higher in the inoculated treatments. Results of present study clearly demonstrated that different isolates of Rhizobium species improved the growth and yield parameters of cotton and thus Rhizobium sp can be effectively utilized as bacterial inoculants in non-legumes.