Seasonal Diversity Status of Plant Growth Promoting Rhizobacteria (PGPR) in Rhizosphere of Fast Growing Native Tree Species, Melia dubia in Tamil Nadu

A study was conducted to determine the seasonal diversity status of different beneficial bacteria viz., Plant growth promoting rhizobacteria (PGPR) from the rhizosphere of M. dubia plantations of Tamil Nadu. Total of 28 PGPR isolates (Azotobacter - 8 isolates; Azospirillum - 9 isolates; PSB - 11 isolates) were recorded from various samples collected from different study locations and identified as members of two species each of Azotobacter and Azospirillum and five species of PSB. Among PSB, four Bacillus species and one Stenotrophomonas species were observed. Clear seasonal pattern was seem on the occurrence and distribution of population density of PGPRs. Population density of Azotobacter was found maximum during April-June (2011), whereas population density of Azospirillum and PSB was found maximum during Oct-Dec (2011). The climatic and edaphic factors influenced the population density of PGPR colonization, but the intensity of their influence varies with the study sites. Soil in all the sites was found acidic, low in available nitrogen, moderate in available phosphorus and high in available potassium. Studies on growth hormone (IAA) production and phosphate solubilization by PGPR isolates further revealed the potentiality of these isolates to be optimized and produced on a large scale as bio-fertilizers for growth enhancement of important native tree species.