We assayed for Chrysanthemum stunt viroid (CSVd) in cultivated chrysanthemum (Chrysanthemum morifolium) collected from 10 prefectures in Japan and 8 wild species (Chrysanthemum spp.) cultivated at the National Institute of Floricultural Science (NIFS), Japan and determined complete nucleotide sequences of CSVd isolates infecting plants. CSVd was detected in 80 of 89 samples of cultivated chrysanthemum, and samples from all prefectures were infected. Since all 8 wild species had CSVd in RT-PCR results, they were recognized as hosts of CSVd, even though no stunt symptoms were observed. Five sequence variants of CSVd were distinguished among the 21 isolates based on the difference of the nucleotide sequences. Mutations were common in the P (pathogenicity) domain. Variant 5 from C. morifolium, and variant 4 from C. yoshinaganthum had different nucleotide sequences from those reported previously. Variant 1 was most frequently detected from samples in 6 prefectures and is assumed to be the predominant CSVd variant distributed in Japan.

Root and stem rot with wilt of above ground parts of cultivated chrysanthemums was first found in Ibaraki, Toyama and Kagawa prefectures, Japan in 2002 and2003. Pythium species were isolated from the diseased tissues and identified as P. dissotocum, P. oedochilum, P. sylvaticum, P. ultimum var. ultimum and asexual strains of P. helicoides based on their morphologies and sequences of rDNA-ITS region. All the Pythium species were strongly pathogenic to chrysanthemums in pot conditions and were reisolated from the inoculated plants. Because Pythium root and stem rot of chrysanthemum has never been reported in Japan, we propose that this is a new disease that can be caused by the five Pythium species.

A new species of Phytophthora was isolated from stem and root rot of chrysanthemum in the Gifu and Toyama prefectures of Japan. The species differs from other Phytophthora species morphologically, and is characterized by nonpapillate, noncaducous sporangia with internal proliferation, formation of both hyphal swellings and chlamydospores, homothallic nature, distinctive intercalary antheridia, and funnel-shaped oogonia. The new species can grow even at 35°C, with an optimum growth temperature of 30°C in V8 juice agar medium. In phylogenetic analyses based on five nuclear regions (LSU rDNA; genes for translation elongation factor 1α, β-tubulin, 60 S ribosomal protein L10, and heat shock protein 90), the isolates formed a monophyletic clade. Although the rDNA ITS region shows a high resolution and has proven particularly useful for the separation of Phytophthora species, it was difficult to align the sequences for phylogenetic analysis. Therefore, ITS region analysis using related species as defined by the multigene phylogeny was performed, and the topology of the resulting tree also revealed a monophyletic clade formed by the isolates of the species. The morphological characteristics and phylogenetic relationships indicate that the isolates represent a new species, Phytophthora chrysanthemi sp. nov. In pathogenicity tests, chrysanthemum plants inoculated with the isolates developed lesions on stems and roots within 3 days, and the symptoms resembled the ones originally observed. Finally, the pathogen's identity was confirmed by reisolation from lesions of infected plants.

In April 2007, coleus (Solenostemon scutellarioides) plants cultivated in a greenhouse in Chiba Prefecture, Japan were observed to have poor growth, with yellowing of the adaxial leaf surface and a gray to black downy growth on the abaxial leaf surface. The causal pathogen was identified as Peronospora belbahrii based on its morphology and rDNA-ITS sequences. Uninfected coleus was inoculated with the pathogen, the original symptoms were reproduced, and the isolate was reisolated. This is the first report of downy mildew of coleus in Japan.

Cutting rot of chrysanthemum was found on cuttings of cv. Jimba No.2 in 2008. The cuttings were imported, then transplanted in Aichi Prefecture. Root development was not initiated in about 30% of the cuttings. The cut stem ends developed black discolouration and decay. When healthy cuttings were the fungus isolated from diseased cuttings, these cuttings developed the same disease symptoms. The characteristics and morphology of the fungal culture were identical to those of Plectosporium tabacinum. We propose that the new disease be named cutting rot of chrysanthemum.