The 16S rDNA, endoglucanase, and hrpB genes were partially sequenced for Asian strains of Ralstonia solanacearum spp. complex, including 31 strains of R. solanacearum and two strains each of the blood disease bacterium (BDB) and Pseudomonas syzygii. Additional sequences homologous to these DNA regions, deposited at DDBJ/EMBL/GenBank databases were included in the analysis. Various levels of polymorphisms were observed in each of these DNA regions. The highest polymorphism (approximately 25%) was found in the endoglucanase gene sequence. The hrpB sequence had about 22% polymorphism. The phylogenetic analysis consistently divided the strains into four clusters, as distinctly shown on the phylogenetic trees of 16S rDNA, hrpB gene, and endoglucanase gene sequences. Cluster 1 contained all strains from Asia, which belong to biovars 3, 4, 5, and N2. Cluster 2 comprised the Asian strains of R. solanacearum (as biovars N2 and 1) isolated from potato and clove, as well as BDB and P. syzygii. Cluster 3 contained race 3 biovar 2 strains from potato, race 2 biovar 1 strains from banana, and race 1 biovar 1 strains isolated from America, Asia, and other parts of the world. Cluster 4 was exclusively composed of African strains. The results of the study showed the distribution and diversity of the Asian strains, which are present in three of the four clusters. The similarity of Asian strains to those in the other regions was also observed.

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Strains of Ralstonia solanacearum, Pseudomonas syzygii, and the blood disease bacterium (BDB) from different countries were tested for polymerase chain reaction amplification of the 282-bp fragment using the primer pair 759 and 760. These 282-bp fragments from 49 strains of R. solanacearum, six strains of P. syzygii, and two strains of BDB were sequenced. A phylogenetic tree was generated based on the sequence alignment. The R. solanacearum strains were divided into three groups. Group I was composed of strains belonging to biovars 3, 4, 5, and biovar N2 from Japan. Most of the strains from this group were of Asian origin except for two strains from Australia and Guyana (GMI 1000), the type strain. Group II was composed of strains belonging to biovars 1 and 2 and biovar N2 from Brazil. Group III was composed of strains belonging to biovar N2 from Japan and the Philippines. All strains of P. syzygii and BDB clustered in group III. Based on nucleotide differences of the 282-bp fragments, restriction enzyme NlaIII was capable of differentiating R. solanacearum strains into the three groups. Restriction analysis of 165 R. solanacearum isolates from the Philippines using NlaIII showed that all biovar 3 and 4 (group 1) strains had restriction fragments of 116 and 166 bp, strains belonging to biovars 1 and 2 (group 2) showed no restriction, and one strain belonging to biovar 2 (group 3) showed restriction fragments of 54 and 228 bp in size. Thus, NlaIII could be used for rapid differentiation of R. solanacearum strains. Additionally, other restriction enzymes, such as McrI, BsiEI, and MnlI could be used to differentiate R. solanacearum strains from P. syzygii strains.

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