Chlorotic leaf spot symptoms of Japanese and European pears, associated with infestation of the Japanese pear rust mite (Eriophyes chibaensis Kadono), have been noticed nationwide in Japan in the last decade. We previously reported detection of pear chlorotic leaf spot-associated virus (PCLSaV), a new emaravirus found in China, from pear orchards in Ibaraki, Niigata, Aichi, and Kumamoto prefectures, Japan. To further elucidate the regional distribution, relationship between the leaf chlorotic symptoms and PCLSaV infection, and the genetic diversity of PCLSaV isolates in Japan, we collected leaf samples of Japanese and European pear varieties with or without chlorotic spots from 13 prefectures from Honshu, Shikoku, and Kyushu regions in 2017, 2019, and 2020 and tested for RNA1–RNA5 of PCLSaV using reverse transcription-polymerase chain reaction. PCLSaV was detected in all the prefectures surveyed, and the chlorotic leaf spots were highly correlated with the presence of PCLSaV. Complete nucleotide sequences of open reading frames encoded by RNA1–RNA5 of the PCLSaV isolates were determined and phylogenetic and nucleotide diversity analyses were performed, which indicated that genetic diversity of the Japanese PCLSaV isolates was quite low compared to the three Chinese isolates reported previously. These results suggest that it appeared recently and rapidly spread in Japan.

In this study, we investigated the suppressive effect of polycarbamate and organic copper against hydrangea bacterial spots associated with Acidovorax valerianellae. The application of polycarbamate significantly suppressed the disease in four of five trials, while organic copper significantly suppressed the disease in two of three trials. We used generalized liner mixed models to evaluate the integrated effect of each of the two fungicides throughout all trials. In our experimental model, the coefficients of polycarbamate and organic copper application in reference to the negative control were −0.70 and −0.90, respectively (p < 0.01). These results indicate that the application of these fungicides can effectively suppress hydrangea bacterial spots. To best of our knowledge, this is the first report that fungicides can suppress disease related to A. valerianellae and will contribute to disease prevention during hydrangea production.

Electrolyzed water has promise for controlling plant pathogen control agents including disinfesting rice seeds; however, the effective component, hypochlorous acid (HA), is unstable, and its efficacy is readily lost upon contact with organic substances. Therefore, weakly acidic hypochlorous acid (waHA) water that retains its activity for a long period was developed. Here, we examined the efficacy of waHA water disinfesting seeds. Treating seeds with waHA water during seed soaking to hasten germination suppressed rice blast, bakanae, bacterial grain rot, bacterial seedling blight and bacterial brown stripe diseases, but treatment before seed soaking suppressed only blast and bakanae diseases. When waHA water, HA electrolyzed water and aqueous NaClO were compared for their effects against several seed-borne pathogens, the waHA water tended to be better than the others at controlling blast and bacterial seedling blight. These results indicate that waHA water can be a practical, effective agent to disinfest rice seed.

In May 2021, okra was found to be infected with a powdery mildew in Okinawa Prefecture, Japan. The fungus associated with foliar symptoms of powdery mildew was identified as Podosphaera xanthii using morphological characteristics of the anamorph and molecular analysis of ITS regions. No chasmothecium was observed. Podosphaera xanthii is proposed as another pathogen causing powdery mildew on okra in Japan.

Sooty blotch was found on Gynura bicolor seedlings in Okinawa Prefecture in 2017. Fungal-like isolates, mainly obtained from the lower leaves, caused similar symptoms on plants sprayed with individual isolates, which were identified as Zasmidium gynurae based on morphological characteristics and sequences of rDNA ITS regions. This is the first report of a disease of G. bicolor caused by Z. gynurae in Japan, and we propose the Japanese name “susuhan-byou” (sooty blotch) of Gynura bicolor.