Saturday, 15 July 2006

Enumeration, Isolation and Identification of Diazotrophic Bacterial Species from Paddy Rice in Korea.

Ui Gum Kang, Yeongnam Agricultural Research Institute, National Institute of Crop Science, P.O.Box 6, Milyang, South Korea

An attempt was made to enumerate the total diazotrophic and heterotrophic bacterial populations from the rhizosphere soils of rice plants, surface sterilized roots and basal portion of stems of Paddy rice varieties cultivated in soils supplied with different doses of N fertilizer. Enumeration indicated that the fertilizer N (150 kg ha-1) with application of compost could promote the growth of both heterotrophic and diazotrophic bacteria. Enumeration of these populations in six different paddy rice varieties applied with 110 kg ha-1 of N showed that malate utilizing spirillum species were dominating compared to Azelaic acid utilizing Burkholderia species and sucrose utilizing Gluconacetobacter species. Selection from the acetylene reducing pellicles led to the isolation of more than three different diazotrophic bacterial groups using three different media. Members of isolates from the first group were further identified as Azospirillum brasilense, Azospirillum lipoferum and Azospirillum amazonense based on the formation of veil like pellicles at the surface of medium, cell shape, colony type, pigmentation on different media and utilization of specific carbon substrates. The second group was preliminarily identified as nitrogen fixing Burkholderia species based on the above mentioned characteristic features. Similarly, the third group was also identified as Gluconacetobacter diazotrophicus. A PCR assay based on the amplification of a nifH specific primer with representative isolates from each group indicated the presence of nitrogen fixing genes. In the partial analysis of 16S rDNA sequence, 4 isolates of 20 representative diazotrophs showed lower similarity than 98%. This result suggested agronomically important paddy rice varieties in Korea harbor different diazotrophic isolates such as Azospirillum spp., Herbaspirillum spp., Burkholderia spp. and Gluconacetobacter spp. Key words : Paddy rice, Isolation, Diazotrophs, nifH, 16S rDNA sequence.

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