Abstract
Rhizobia are vital for nitrogen input, fertility of soil and legume plant growth. Knowledge on rhizobial diversity from arid and semiarid areas is important for dry land agriculture in the context of climatic change and for economic utilization. This study provides morphological, biochemical, stress tolerance and plant growth promoting characteristics of fifteen rhizobial isolates from the nodules of same number of wild legumes and one isolate from cultivated Arachis hypogea from semi-arid region, Tirupati. The bacterial isolates were confirmed as rhizobia based on colony morphology and biochemical tests. Based on the colour change of YMA-BTB medium, eight isolates were identified as slow growers and six were fast growers. The isolates differed in growth pattern, colony morphology, antibiotic resistance at higher concentrations and uniformity in utilization of carbon and nitrogen sources. The isolates are tolerant to NaCl up to one percent, displayed normal growth at temperatures 28℃ - 30℃, at neutral pH and poor growth at pH 5and 9. The isolates varied in the production of EPS and IAA, positive for phosphate solubilization and siderophore formation. This functional diversity displayed by the isolates can be utilised for the legume crop production by cross inoculation.
Highlights
Symbiotic nitrogen fixation, involving legumes and rhizobia is of considerable economic and ecological significance
Rhizobia are a group of soil bacterial species that infect leguminous plants leading to the formation of special type of organs called nodules, where nitrogen fixation takes place
This study aimed at evaluating the phenotypic diversity, stress tolerance and plant growth promoting characteristics of rhizobial isolates from wild legumes of semiarid habitat, Tirupati, India
Summary
Symbiotic nitrogen fixation, involving legumes and rhizobia is of considerable economic and ecological significance. The nitrogenase enzyme complex of bacterioids i.e. symbiotic form of rhizobia supplies constant source of reduced nitrogen to the legume host and intern, receives the nutrients and energy. This symbiotic process occurs on all continents and accounts for a fourth of the nitrogen fixed annually on earth [1], has become important component of sustainable organic agriculture. Establishment of effective symbiosis depends on cross talk between plant host and rhizobia at different stages, starting from the initial recognition of partners, through functional nodule formation and nitrogen reduction [3]
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