Characterization and Improvement of Plant Growth Promoting Rhizobacteria (PGPR) and Their Effects on Cereal Production

Abstract

Identification of genes responsible for indoleacetic acid (IAA) production in plant growth promoting bacteria (PGPB) was carried out by using plus 2 DNA probe. Out of 18 strains tested, 12 strains tested, 12 strains were found to harbor IAA producing genes. Protein profile of total bacteria proteins proved useful for differentiation of bacterial strains up to species level. For differentiation of the bacterial isolates, REP, ERIC and random primers were used in polymerase chain reaction (PCR). Unique pattern of PCR products obtained from each isolate confirmed that the isolates were different strains and were not “re-isolate” obtained from the same environment. Identification and qualification of plant growth hormones IAA and gibberellic acid (GA), produced by PGPR was carried on high pressure liquid chromatograph (HPLC). Some Azospirillum strain produced both IAA and GA while none of the Enterobacter sp.test produced the growth hormones. Azoarcus strain K-1 produced higher amount of GA and Azospirillum strain ER-2 produced higher amount of IAA. Indoleacetic acid production increase with the age of bacterial culture while decrease in production of GA was noted at the later growth stages. Pure IAA and GA in the concentration range of 1-2 μg/ml increase root area and plant biomass of rice and wheat. Among PGPR strain tested, pseudomonas 96-51 and its extract containing hormones increased root area. Inoculation with diazotrophic bacterial strains contributed higher amount (up to 28%) of nitrogen to rice plants. Inoculation also increased the number of tillers, grains and straw weight.