Characterization of plant growth promoting rhizobacteria (PGPR) and their effect on seed germination seedling vigour and growth of cotton

Sterilized seeds (with 0.01 % HgCl2) of four varieties of cotton viz. NIBGE-1, Karishma-99, NIAB-98 and FH-901 were inoculated with known number of viable cells of four PGPR strains viz. Azospirilluin sp. ER-20 (from wheat) Pseudomonas sp. 96-51 (from kallar grass), Pseudomonas sp. stutzeri K-1 (form wheat-rice) and Azotobacter sp. S-8 (isolated from cotton rhizosphere) with three replications in addition to un- inoculated controls. All the isolates were gram negative, rod shaped, few were non motile, only S-8 slowly motile and the rest were motile with different growth rate. For nitrogen activity, all the isolates were nitrogen fixers with different nitrogen fixing potential. Qualitative indoles acetic acid producing ability of all the isolates was tested by calorimetric method and five isolates were found IAA producer. No isolate was found to be phosphate solubilizer. Germination studies were conducted in sterilized sand plates and sterilized ten seeds were sown in each plate. Although no inoculation treatments showed significant results but varietal effect was significant and cotton variety FH-901 showed maximum germination percentage (94 %). In case of shoot growth, shoot fresh and dry weight was significantly increased by bacterial inoculation treatments Azospirillum sp. ER-20 and Pseudomonas sp. 96-51 with cotton variety Karishma-99. Percent increase in shoot fresh and dry weight by inoculation treatments Pseudomonas sp. 96-51 was 78 % and 38 %, respectively, compare (without nitrogen) and that of Azospirillum sp. ER-20 was 69 % and 23 % respectively compared to control (without nitrogen). For root growth, root fresh weight increased by inoculation treatments Pseudomonas stutzeri K-1 with cotton varieties Karishma-99 and FH-901, Aeudomonas sp. 96-61 with FH-901 and Azotobacter sp. S-8 with Karishma-99 variety. Similarly root length, root width and root area were significantly increased by inoculation treatment Pseudomonas sp. 96-51 with different cotton cultivars. Root width increased significantly by the same inoculation treatment with, Karishma- 99 and NIBGE-1 and Azotobacter sp. S-8 with Karishma-99 and both treatments showed 25% increase in root width compared to control without nitrogen. Similar, results were recorded in root area. Total biomass was increased by inoculation Pseudomonas sp. 96-61 with cotton cultivars, NIAB-98 which is statistically similar to same inoculation treatment with Karishma-99 and FH- 901. Azospirillum sp. ER-20 with Karishma-99, Pseudomonas stutzeri K-1 with FN-901 and. Azotobacter sp. s-8 with Karishma-99 inoculation treatment Pseudomonas sp. 96-51 showed maximum percent increase (73 %) in biomass compared to control without nitrogen. Significant results were observed in nutrient up take by inoculation treatment compared to control. Shoot nitrogen contents were increased by inoculation Azospirillum sp. ER-20 with Karishma-99. Shoot potassium (K+) concentration was increased significantly by Pseudomonas stutzeri K-1 with NIAB-98 and calcium (Ca++) concentration increased by Azospirillum ER-20 with FH-901. From the present research studies it is concluded that plant growth promoting Rhizobacteria (PGPRs) have significant effect on seedling vigour and growth of cotton. Although the four PGPR strains have no effect on seed germination but seedling vigour and growth was significantly enhanced. In shoot growth, it one strain significantly increased shoot fresh and dry weight, then other strains had pronounced effect on shoot length. Similar results were recorded in root growth and nutrient uptake and in some cases all the four PGPR strains had significant effect on different morphophysiological parameters.