A new disease, brown leaf spot of gentian, Gentiana scabra var. buergeri (Miq.) Maxim. was first found in 1984 in Okayama Prefecture, and then in Iwate Prefecture, Japan. The spots are first pale brown, then turn to grayish white, often with a purplish brown border. Diseased leaves usually dry out without early defoliation. Often flower buds are infested. Fruiting bodies of a fungus develop on the leaf spots and have a unique morphological development. Spraying a suspension of conidia-like propagules from the fruiting bodies or placing a disc of the isolated fungal colony on the leaves resulted within 1 to 2 weeks in the appearance of the leaf spot symptoms the same as in field. The pathogen was similar to hyphomycetous genus Mycochaetophora Hara et Ogawa established in 1931 for the fungus that causes circular leaf spot of Zelkowa serrata (Thunb.) Makino. But Zelkowa serrata did not develop any disease after inoculation with the fungus isolated from gentian. Because the sizes of the sporophore and conidium of the gentian fungus also differs from the Mycochaetophora pathogen of Zelkowa, the present fungus was treated as a new species of the genus Mycochaetophora, and named M. gentianae Tak. Kobay., Kasuyama et Nasu.
In a survey from 2001 through 2006 of host range, distribution and other factors affecting powdery mildew diseases on various plant species in seven mountainous regions of Akita Prefecture (including the environs of Akita and Daisen cities), 126 plant species representing 48 families were recorded as host plants. Most host species in the northern region of Akita Prefecture were in the Caprifoliaceae, whereas in the central and the southern regions they were mostly in the Compositae. Nine species were newly recorded as host plants in Japan, with two species each in the Rosaceae, Caprifoliaceae and Compositae, and one species each in the Guttiferae, Araliaceae, and Ericaceae. Powdery mildew fungi belonging to 10 genera (7 genera in a new taxonomic system) were isolated from host plants, predominantly from genera Uncinula (Erysiphe section Uncinula and Parauncinula novo systema) and Microsphaera (Erysiphe section Microsphaera). The numbers of diseased host plants varied considerably by region. Akita Prefecture, where more than 30% of the potentially susceptible host species were infected, had three characteristic features: average rainfall from June through September was less than 166 mm/month; average wind speed from June through September was greater than 1.2 m/s; and average soil calcium exceeded 1900 mg/kg. Disease incidence was low in the Oga region, where soil calcium was as low as 1400 mg/kg, despite having the other criteria for high incidence. Therefore, the main factor affecting disease incidence may be soil calcium.
In 2005 and 2006, cucumber powdery mildew caused by Oidium subgenus Reticuloidium was found in semiforcing and open-field cultures in 11 fields in five cities and two towns in the Tama area of Tokyo. This subgenus affected the cucumber plants from the beginning of May to the middle of June. After this period, Oidium subgenus Fibroidium infected the plants. The concomitant presence of both subgenera at the initiation of the disease was rare. Oidium subgenus Reticuloidium was estimated to cause 21.8%~39.0% of the total damage to the leaves, and the disease severity was estimated to be 5.8~12.8 in two fields. The morphological features of the isolates from Tokyo were in agreement with those reported in the literature for the subgenus; however, the observed foot-cell length differed from that reported previously. The susceptibility of cucumber varieties to subgenus Reticuloidium was similar to that to the subgenus Febroidium, with the exception of the variety “Yuusen.”
Two strains of ‘Candidatus Phytoplasma asteris’ (onion yellows phytoplasma: OYP and Cryptotaenia japonica witches’ broom phytoplasma: CJWP) were detected by PCR from the nonvector leafhopper (Nephotettix cincticeps) that had fed on phytoplasma-infected plants or had been injected with one of the phytoplasmas. In all experiments, each phytoplasma was detected from the mid-gut, abdomen, thorax, head and salivary glands of insects after acquisition feeding or injection. However, neither phytoplasma was transmitted after inoculation feeding. This report is the first that phytoplasmas can pass through the mid-gut wall and reach the salivary glands of a nonvector leafhopper that had fed on phytoplasma-infected plants.
An outbreak of anthracnose on Indian mulberry (Morinda citrifolia L.) was recorded in Okinawa Prefecture in 2006. Abundant conidial masses formed on the surface of brown spots or zonate brown spots on leaves. A Colletotrichum species was isolated from the diseased leaves and stems, and typical symptoms were reproduced after inoculation of either wounded or intact leaves. The causal agent was identified as Colletotrichum gloeosporioides based on morphological characters and growth temperature.