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Surface colonization by Azospirillum brasilense SM in the indole‐3‐acetic acid dependent growth improvement of sorghum
Author(s) -
Kochar Mandira,
Srivastava Sheela
Publication year - 2012
Publication title -
journal of basic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.58
H-Index - 54
eISSN - 1521-4028
pISSN - 0233-111X
DOI - 10.1002/jobm.201100038
Subject(s) - azospirillum brasilense , auxin , root hair , rhizosphere , microbial inoculant , biology , bacteria , shoot , sorghum , elongation , rhizobacteria , colonization , indole 3 acetic acid , botany , inoculation , horticulture , microbiology and biotechnology , biochemistry , agronomy , gene , materials science , ultimate tensile strength , metallurgy , genetics
The key to improving plant productivity is successful bacterial‐plant interaction in the rhizosphere that can be maintained in the environment. The results presented here confirm Azospirillum brasilense strain SM as a competent plant growth promoting bacterium over mid‐ and long‐term associations with sorghum. This study establishes that plant growth can be directly correlated with the associated bacterium's indole‐3‐acetic acid (IAA) production capability as IAA over‐expressing variants, SMp30 and SMΔi3‐6 fared better than the wild type strain. The auxin antagonist, p‐chlorophenoxy isobutyric acid confirmed the role of bacterial IAA in plant growth promotion and verified the presence of larger amount of IAA available to the seeds on inoculation with IAA over‐expressing mutants. Microscopic analysis identified the bacterial association at root tips, root‐shoot junction and elongation zone and their surface colonizing nature. Scanning electron microscopy identified larger number of root hairs and extensive exopolysaccharide covering in comparison to untreated ones. In addition, vibroid‐shaped Azospirilla attached by means of fibrillar material were dispersed along the elongation zone. The notable difference with IAA over‐expressing variants was enhanced number of root hairs. Thus, the variant strains may be more efficient surface colonizers of the sorghum root and used as superior bio‐inoculants for improving plant productivity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)