Biochemical Characteristics and Plant Growth Promoting Properties of Zinc Solubilizing Bacteria Isolated from the Rhizosphere Soil of Paddy (Oryza sativa L.)

Zinc is one of the trace elements with growth-promoting effects and plays a major role in many processes related to enzymatic functions, protein synthesis and metabolic path­ways. Low zinc supply limits the rice plant's ability to convert amino acids to proteins. Zinc-solubilizing bacteria act as natural bio-fortifiers that can solubilize the unavailable form of zinc by secreting organic acids, siderophores, and other chelating compounds. Hence, 32 zinc solubilising bacterial isolates were collected from the rhizosphere soil of paddy crop in 21 villages of Kurnool, Prakasam, Guntur and Anantapur districts of Andhra Pradesh by using insoluble source of zinc. These isolates were verified for plant growth promoting properties viz., zinc solubilization, phosphate solubilization, potassium release, exopolysaccharide production, indole acetic acid production, siderophore production and then subjected to standard biochemical tests including starch hydrolysis, hydrogen sulphide production, Indole production, catalase production, oxidase synthesis, gelatine liquification, methyl red reaction, Vogues Proskauer test reaction, citrate utilization and ammonia production in the Department of Agricultural microbiology, Advanced Post Graduate Centre, ANGRAU, Lam, Guntur. Two isolates, ZnKJJ-4 (Zinc solubilizing isolate from soil sample - 4 of Kurnool Dist., Jupadu bunglow Mandal and village) and ZnPGG-1 (Zinc isolate from soil sample - 1 of Prakasam Dist., Giddaluru Mandal and village) showed the highest efficiency with respect to plant growth promoting activities. Therefore, these two isolates (ZnKJJ-4, ZnPGG-1) were selected for further evaluation in direct sown paddy crop.