Isolation and characterization of KDML105 aromatic rice rhizobacteria producing indole-3-acetic acid: impact of organic and conventional paddy rice practices.

Indole-3-acetic acid (IAA) synthesis is a major property of rhizosphere bacteria. The IAA-producing ability of rhizobacteria may be influenced by agricultural management. We therefore evaluated the IAA-producing potential of rhizobacteria isolated during organic rice farming (ORF) and conventional rice farming (CRF) in Thung Kula Rong Hai areas of Thailand. The results indicated that ORF gave a significantly higher percentage of IAA producers (95.8%) than CRF (69.9%). The average IAA values of the ORF isolates were around two times higher than those of the CRF isolates both in the absence (12.8 and 5.8 μg IAA mL-1 , respectively) and presence of L-tryptophan (L-Trp) (35.2 and 17.2 μg IAA mL-1 , respectively). The 16S rRNA gene sequence analysis indicated that the 23 selected isolates belonged to 8 different genera-Sinomonas sp., Micrococcus sp., Microbacterium sp., Fictibacillus sp., Bacillus sp., Burkholderia sp., Leclercia sp. and Enterobacter sp. Interestingly, only three ORF isolates i.e., ORF15-20 (Micrococcus sp.), ORF15-21 (Sinomonas sp.) and ORF15-23 (Sinomonas sp.), exhibited high IAA production ability without L-Trp (128.5, 160.8 and 174.7 μg IAA mL-1 , respectively). Meanwhile, a slight decrease in IAA production with L-Trp was noticed,suggesting the L-Trp was not used for the IAA synthesis of these isolates. Biopriming with rhizobacterial isolates significantly enhanced the rate of germination of KDML 105 rice seeds compared to the control.