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Subject: Microbiology × Author: BALNATAH, URVASHI × End date: 2016 × Start date: 2010 × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    STUDIES ON PLANT GROWTH PROMOTING RHIZOBACTERIA ASSOCIATED WITH STRAWBERRY (Fragaria x ananassa)
    (2013) BALNATAH, URVASHI; SHIRKOT, C.K.
    ABSTRACT Plant hormones are chemical messengers that affect a plant's ability to respond to its environment. Hormones are organic compounds that are effective at very low concentration; they are usually synthesized in one part of the plant and are transported to another location. Botanists recognize five major groups of hormones: auxins, gibberellins, ethylene, cytokinins, and abscisic acid. IAA (indole-3-acetic acid) is the member of the group of phytohormones and is generally considered the most important native Auxin . It functions as an important signal molecule in the regulation of plant development including organogenesis, tropic responses, cellular responses such as cell expansion, division, differentiation, and gene regulation. Therefore, the objective of the present study was to isolate and screen the IAA producing rhizobacteria from strawberry (Fragaria×ananassa) and to optimize cultural conditions for maximum production of IAA. Fifty one, IAA producing bacterial isolates (thirty five rhizospheric and sixteen endophytic) were selected (by replica plating technique) from the rhizosphere soil and roots of the four different sites of strawberry. These isolates exhibited variability in growth on nutrient agar, Chromo azurol–S, Pikovskaya’s and Nitrogen free media. Variation was also observed in their plant growth promoting (PGP) activities: IAA production (quantitative), Siderophore (qualitative and quantitative) production varied among isolates. Variation was also observed in type (Hydroxamate, carboxylate, catecholate) of siderophore produced and phosphate solubilization. All the fifty one bacterial isolates exhibited antifungal activity against Phytopathora sp. Out of fifty one isolates, eleven were further screened for IAA production by varying the growth culture conditions, further studies were carried out with isolate Na4(1) which produced 55µg/ml of IAA under un-optimized culture conditions. Optimizing the culture conditions after 72 h of incubation at 35oC, at pH 7 and 0.1% tryptophan concentration resulted in significant increase in IAA production production (65µg/ml) by isolate Na4(1), identified as Bacillus firmus on 16S rDNA analysis. IAA producing bacterial isolates were evaluated for growth promotion of strawberry plants under net house conditions. The present study, therefore, suggests that the use of IAA producing bacteria as bio-inoculants that might be beneficial for raising quality strawberry plants in long term and to develop cost effective ecofriendly sustainable system in the management of horticultural problems.