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Tamil Nadu Agricultural University (2014)

Assessment of functional microbial diversity in the rhizosphere of selected semi arid tropicalgrasses

Sarathambal C.

Titre : Assessment of functional microbial diversity in the rhizosphere of selected semi arid tropicalgrasses

Auteur : Sarathambal C.

Université de soutenance : Tamil Nadu Agricultural University

Grade : Doctor of Philosophy (PhD) in Agricultural Microbiology 2014

Résumé partiel
Biological nitrogen fixation by plant-associated bacteria is eco-friendly and has been effectively exploited for crop plants including legumes. Although associations of diazotrophic bacteria with non-leguminous plants such as grasses have been known for decades, they have been poorly - studied. Weedy grass species normally thrive in adverse conditions and act as potential habitats for the diverse groups of elite bacteria with multiple beneficial characters remains unexplored. A more complete understanding of the diversity and functioning of diazotrophic microorganisms, especially those that have symbiotic relationships with grass species is of great value for agricultural research and application. Hence, the present investigation is focused to identify and characterize the unexplored culturable rhizospheric and endophytic diazotrophic bacterial diversity of selected grass species of India. Based on their dominance in each physiological region of the country, a total of 10 different grass species (Brachiaria reptans, Cenchrus glaucus, Saccharum spontaneum, Panicum repens, Cyperus rotundus, Dactyloctenium aegyptium, Chloris barbata, Oryza rufipogon, Cyanodon dactylon and Setaria verticillata) along with rhizosphere soils were selected for the present investigation. The physio-chemical and biological properties of samples analysed and showed significant difference among the regions.A total of 60 diazotrophic isolates from rhizosphere and 21 putative endophytic isolates were obtained from 10 grasses. A total of 30 rhizospheric and 20 endophytic diazotrophic isolates were selected based on their growth on N- free medium, total nitrogen content in the medium and ammonia excretion. Among the isolates, highest nitrogenase activity were exhibited by isolate OR3 (172.25 ±13.95 n moles of ethylene mg-1 of protein h-1 ) isolated from Oryza rufipogon. Among the endophytic diazotrophs, highest ARA activity was found in CGE3 (171.45 ±11.80 n moles of ethylene mg-1 of protein h-1 ) isolated from Cenchrus glaucus. The intrinsic antibiotic resistance and carbon-substrate utilization profiling of the selected isolates showed remarkable difference among them, forming seven different clusters

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