Flavonoids and growth hormones influence endophytic colonization and in planta nitrogen fixation by a diazotrophic Serratia sp in rice

Several endophytic diazotrophs were isolated from cultivars of rice and screened for their diazotrophy by nitrogenase assay and amplification of partial nifH gene. Ability of one of the diazotrophic endophytes, Serratia sp. (isolate EDA2 from cultivar ADT36) to colonize the rice seedlings grown in the presence of flavonoids and growth hormones, under gnotobiotic condition was assessed in cultivar ADT36 using a strain marked with transposon-based egfp and Km(r). The endophytic colonization was monitored through re-isolation from different parts of rice seedlings in LB+Km plates. Addition of the flavonoids quercetin and diadzein to the growth medium increased the extent of endophytic colonization of the conjugant in rice seedlings by colonizing throughout the plant. Population and in planta nitrogenase activity of Serratia in rice seedlings were significantly increased by addition of flavonoids, quercetin and diadzein, whereas growth hormones, IAA and NAA reduced the efficiency of Serratia. The inoculation of Serratia sp. with flavonoids increased the plant biomass and biochemical constituents of rice seedlings under controlled condition.