Isolation and Characterization of Plant Growth-Promoting Actinomycetes from the Rhizosphere of Azadirachta indica
Keywords:
Azadirachta indica, actinomycetes, rhizosphere, plant growth-promoting microorganisms, phosphate solubilization, indole-3-acetic acidAbstract
Actinomycetes are an important group of rhizosphere microorganisms that contribute to nutrient cycling and plant growth through diverse metabolic activities. The present study aimed to isolate and characterize culturable actinomycetes from the rhizosphere of Azadirachta indica and evaluate their qualitative plant growth-promoting attributes. Rhizosphere soil samples were processed by the serial dilution spread plate technique on Starch Casein Agar, resulting in the isolation of eight morphologically distinct actinomycete isolates (ACN01–ACN08). The isolates were characterized on the basis of morphological, physiological and biochemical characteristics. Considerable phenotypic diversity was observed among the isolates with respect to colony pigmentation, mycelial structure and physiological characteristics. All isolates exhibited positive catalase, oxidase, starch hydrolysis, urease and citrate utilization reactions, whereas differences were observed in hydrogen sulfide production, methyl red reaction and salt tolerance. Qualitative screening of plant growth-promoting attributes revealed that six isolates exhibited phosphate-solubilizing activity, four showed zinc and potassium solubilization, seven produced indole-3-acetic acid (IAA), and six produced ammonia. Among the recovered isolates, ACN02, ACN05 and ACN07 expressed multiple plant growth-promoting attributes. Overall, the findings demonstrate that the rhizosphere of Azadirachta indica harbours phenotypically diverse actinomycetes with multiple plant growth-promoting characteristics and highlights the potential of this ecological niche as a source of beneficial microorganisms for future agricultural applications.
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