Identification of predominant epiphytic and endophytic bacterial isolates in rice seeds effective for enhancement of seed germination and plant growth

During rice growing season, the symptomless rice seeds from different paddy fields in Guilan province, Iran, were collected. After isolation of epiphytic and endophytic bacteria, 39 isolates including 19 epiphytes and 20 endophytes were selected based on the predominant characteristics. Five Operational Taxonomic Units (OTUs) were obtained based on PCR-RFLP of 16S r-DNA in these isolates. According to biochemical tests and partial sequencing of 16S-rDNA, in both epiphyte and endophyte bacteria of rice seeds, the most populated OTUs (V and II) were identified as Pantoea ananatis and Pseudomonas oryzihabitans, respectively. Six representative isolates from these two OTUs were selected to be evaluated for their abilities for rice seed germination and growth enhancement. Among them, P. oryzihabitans was not beneficially effective. However, JpB1 isolate of P. ananatis was considered to be the most effective plant growth promoting isolate, since it showed stable beneficial effects on most surveyed characteristics in both rice seed germination and growth enhancement experiments.  Although, OpB3 isolate of P. ananatis produced IAA in higher amount and solubilized phosphate more than the other isolates followed by JpB1 and P. ananatis L3pB3, it was not beneficially effective on rice seed germination.