Development of Plant Growth Promoting Rhizosphere Microflora as Inoculants for Walnut (Juglans regia L.)

Rhizosphere microbial composition of walnut plants (Cultivar SKAU-W-0035) was studied to select the predominant and efficient isolates of plant growth promoting rhizobacteria as microbial inoculants. Rhizosphere of walnut was found to be inhabited by bacteria, fungi and actinomycetes with maximum population in June and minimum in December. The most predominant microorganisms in the walnut rhizosphere were species of Azotobacter, Azospirillum, Bacillus, Pseudomonas, Aspergillus and Penicillium. Three isolates of each predominant bacterium were screened for plant growth promoting activities. Azotobacter (AZB III), Azospirillum (AZS II), Bacillus (BAC I) and Pseudomonas (PS II) were found to be efficient isolates owing to their ability to produce ammonia, IAA, HCN, antagonasis and phosphorus solubilizing activity. Best growth of all three selected isolates was recorded in nutrient broth at pH 7 and temperature of 300C. The selected isolates were mass-multiplied in nutrient broth for 72 hrs in pilot scale fermentors and mixed with various solid carriers. Shelf life of the cultures was determined by counting the population at 2, 3 and 6 month interval. Lignite was found to be the best carrier for Azotobacter, Azospirillum and Pseudomonas, whereas peat was most suitable carrier for Bacillus.