ALTITUDINAL VARIATIONS IN RHIZOBIUM, PLANT GROWTH PROMOTING RHIZOBACTERIA (PGPR) AND PHOSPHORUS SOLUBILIZING BACTERIA (PSB) IN POTOHAR REGION

Abstract

Soil-dwelling microorganisms are diverse, and interactions with plants vary with respect to environmental heterogeneity, latitude and altitude. At high altitude the microbes have to cope with many environmental and climatic stresses hence develop adaptive mechanisms to withstand the calamities of the environment. The present investigation was carried out to investigate the altitudinal effects on the Plant Growth Promoting Rhizobacteria (PGPR) isolated from rhizosphere soil of wheat and maize grown at two altitudes i.e. Kahuta (1666 m.a.s.l) and Narh (2400 m.a.s.l) of potohar region. The Plant growth Promoting Rhizobacteria (PGPR) were identified on the basis of colony morphology and carbon/nitrogen source utilization pattern determined by QTS (Quick Test System), phytohormone production and 16S rRNA sequence analysis and were found to belong to Rhizobium, Azospirillum and Pseudomonas spp. The Azospirillum was also isolated from the roots of wheat and maize grown at two altitudes. The analysis of rhizospheric soil of both the altitudes revealed that the soil of Narh (2400 m.a.s.l) was comparatively acidic in nature and exhibited higher concentration of metals as compared to the soil of Kahuta (1666 m.a.s.l). The microbial isolates of the high altitude of Narh have shown less utilization of C/N (Carbon/Nitrogen) sources than the isolates of low altitude of Kahuta. The isolates of low altitude have shown higher survival efficiency and greater production of phytohormones .The PGPR from low altitude were more efficient in the production of growth promoting phytohormones (gibberellic acid & Indole -3-Acetic Acid) but the content of stress hormone, Abscisic Acid (ABA) of the isolates of high altitude was significantly higher than that of the isolates of low altitude. Rhizobium was used as bio-inoculant on the mungbean grown in pots under axenic condition in green house while Azospirillum and phosphorus solubilizing bacteria (PSB) isolates were used to inoculate maize. The roots and leaves of the inoculated plants showed greater production of gibberellic acid and Indole-3Acetic Acid. The Azospirillum isolated from roots and rhizospheric soil of low altitude has shown higher content of gibberellic acid & Indole-3Acetic Acid than the Rhizobium and phosphorus solubilizing bacteria (PSB). On the other hand the Abscisic Acid (ABA) content of leaves and roots of the plants inoculated with the isolates of high altitude of Narh was significantly 14higher. The amount of phytohormones production was greater in Azospirillum than that of the other two isolates. The growth promoting effects of the three PGPR isolates with respect to root and shoot growth of maize and mungbean were significantly higher than that from higher altitude. The isolates from higher altitude on the contrary, have great potential to tolerate the heavy metal stress and showed higher resistance to antibiotics. Diversity of PGPR varied at two altitudes. In the rhizospheric soil of wheat grown at Kahuta two more PGPR, Oceanobacillus profundus and Bacillus cereus were indentified while those from Narh were Bacillus sp. TSAWB and Alcaligenes sp. It is inferred that microbes isolated from the rhizosphere of wheat and maize grown at low altitude of Kahuta can be used as inocula for crop improvement and higher yield in future while the microbes of high altitude of Narh can be used as bio-inoculant in the stressed condition as they can thrive better in stressful environment.