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 center dot 8%) than CRF (69 center dot 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 center dot 8 and 5 center dot 8 mu g IAA ml(-1), respectively) and presence of L-tryptophan (L-Trp) (35 center dot 2 and 17 center dot 2 mu g 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 center dot 5, 160 center dot 8 and 174 center dot 7 mu g IAA ml(-1), respectively). Meanwhile, a slight decrease in IAA production with L-Trp was noticed, suggesting that 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.

Automated summary

The study evaluated the IAA-producing potential of rhizobacteria isolated during organic rice farming (ORF) and conventional rice farming (CRF) in Thailand, showing that ORF had a significantly higher percentage of IAA producers compared to CRF. Analysis of the isolates revealed that certain bacteria, such as Micrococcus sp. and Sinomonas sp., exhibited high IAA production ability even without the presence of L-tryptophan.