Approved strains of kiwifruit bacterial canker pathogens

In many kiwifruit-producing countries including Japan, bacterial canker disease has become a serious problem, causing major damage. The causal bacterium (Pseudomonas syringae pv. actinidiae) is now classified into five biovars (biovars 1, 2, 3, 5 and 6) based on the differences in various phenotypes and genotypes. In addition, it is becoming clear that repertories of pathogenicity-related genes and virulence toward kiwifruit differ among biovars. Of these, four biovars (biovars 1, 3, 5 and 6) have been confirmed to exist in Japan, causing canker disease on Actinidia chinensis, A. deliciosa and A. arguta.

The NARO Genebank has a lot of strains belonging to the four biovars confirmed to exist in Japan. They were characterized based on phenotypic tests, PCR assays, MLSA and comparative genome analyses, showing that some biovars have extremely rich variation and can be subdivided into several groups. Therefore, for each biovar/group, we chose some strains with typical characteristics as the approved strains and decided to show them here with related information.

• Reference Sawada, H. and Fujikawa, T. (2019). Genetic diversity of Pseudomonas syringae pv. actinidiae, pathogen of kiwifruit bacterial canker. Plant Pathology 68: 1235-1248. [10.1111/ppa.13040]
• Reference Fujikawa, T. and Sawada, H. (2019). Genome analysis of Pseudomonas syringae pv. actinidiae biovar 6, which produces the phytotoxins, phaseolotoxin and coronatine. Sci. Rep. 9: 3836. [10.1038/s41598-019-40754-9]
• Reference Fujikawa, T. and Sawada, H. (2016). Genome analysis of the kiwifruit canker pathogen Pseudomonas syringae pv. actinidiae biovar 5. Sci. Rep. 6: 21399. [10.1038/srep21399]
• Reference Genka, H., Baba, T., Tsuda, M., Kanaya, S., Mori, H., Yoshida, T., Noguchi, M.T., Tsuchiya, K. and Sawada, H. (2006). Comparative analysis of argK-tox clusters and their flanking regions in phaseolotoxin-producing Pseudomonas syringae pathovars. J. Mol. Evol. 63: 401-414. [10.1007/s00239-005-0271-4]
• Reference Sawada, H., Takeuchi, T. and Matsuda, I. (1997). Comparative analysis of Pseudomonas syringae pv. actinidiae and pv. phaseolicola based on phaseolotoxin-resistant ornithine carbamoyltransferase gene (argK) and 16S-23S rRNA intergenic spacer sequences. Appl. Environ. Microbiol. 63: 282-288. [10.1128/aem.63.1.282-288.1997]

• *1 The presence or absence of tox island [genomic island containing phaseolotoxin biosynthesis gene cluster (argK-tox cluster)] was investigated with PCR assays targeting argK, argD, desI and amtA and with genome analyses.
• *2 Phaseolotoxin production was confirmed by means of growth inhibition assays using sensitive Escherichia coli strains.
• *3 The presence or absence of coronatine biosynthesis gene cluster was investigated with PCR assays targeting cfl, corR and cmaU and with genome analyses.
• *4 The presence or absence of Pac_ICE1, Pac_ICE2 and Pac_ICE3 was investigated with PCR assays targeting the respective internal regions and with genome analyses.