Evaluation of plant growth promoting and colonization ability of endophytic diazotrophs from deep water rice

A study of the diversity of endophytic bacteria present in seeds of a deepw ater rice variety revealed the presence of seven types of BOX-PCR fingerpri nts. In order to evaluate the plant growth promoting potential the presence of nitrogenase, indole acetic acid production and mineral phosphate solubi lization were estimated in the representative BOX-PCR types. The seven repr esentatives of BOX-PCR types produced indole acetic acid, reduced acetylene and showed specific immunological cross-reaction with anti-dinitrogenase r eductase antibody. Only four types showed mineral phosphate solubilizing ab ility. Comparison of cellulase and pectinase activities showed differences among different BOX-PCR types. PCR fingerprinting data showed that one stra in isolated from the surface sterilized seeds as well as the aerial parts o f the seedlings of rice variety showed low cellulase and pectinase but rela tively high ARA. On the basis of 16S rDNA nucleotide sequence and BIOLOG sy stem of bacterial identification, this strain was identified as Pantoea agg lomerans. For studying the endophytic colonization this strain was genetica lly tagged with the reporter gene, gusA. Histochemical analysis of the seed ling grown in hydroponics showed that the tagged strain colonized the root surface, root hairs, root cap, points of lateral root emergence, root corte x and the stelar region. Treatment of the roots with 2,4-D produced short t hickened lateral roots which showed better colonization by P. agglomerans. (C) 2001 Elsevier Science B.V. All rights reserved.