The isolates of Rhizoctonia solani anastomosis group (AG)-1 IA were known for the pathogens of the Gramineae and Legum plants. Recently, however, AG-1 IA isolates were obtained from several Brassicaceae plants including cabbage in Vietnam. Therefore, this study tested the pathogenicity of three Japanese AG-1 IA strains isolated from cabbage, rice, and timothy to the cabbage plant. All three strains showed pathogenicity, although the virulence of cabbage strain was very weak, presumably as a result of its long-term preservation. These results suggest that most Japanese AG-1 IA strains show pathogenicity to cabbage plants.

Damping-off symptoms were observed in four commercial cabbage fields in Iwate, Japan, from May to June 2021. Four fungal isolates from the diseased plants were identified as Rhizoctonia solani anastomosis group (AG)-2-1 and AG-2-2 IV. They were confirmed as pathogens, based on the morphological traits, temperature-dependent growth characteristics, hyphal anastomosis reaction, genome analysis using specific PCR primers, rDNA-ITS sequences, and pathogenicity tests. This is the first report of damping-off on cabbage caused by R. solani AG-2-1 and AG-2-2 IV in Japan. Therefore, we propose that they are the pathogens of this disease.

Dydimella bryoniae and Fusarium graminearum have been known as the two common pathogens of rotted winter squash fruit during storage in Hokkaido, Japan. In this study, we revealed that five additional pathogens, causing fruit rot. They were identified based on morphology and rDNA-ITS sequences as Alternaria sp., Arthrinium arundinis, Botrytis cinerea, Rhizopus arrhizus, and R. stolonifer.

In 2018, approximately 80% of the apple cultivation areas in Hokkaido were affected by apple scabs. Furthermore, in 2017, DMI-resistant strains of Venturia inaequalis were found in Japan. Therefore, we investigated the sensitivity of V. inaequalis in Hokkaido to DMI. Eighty-two isolates were collected from the apple orchards in Hokkaido. We conducted culture medium tests for difenoconazole and fenarimol sensitivity, and the half maximal effective concentration (EC₅₀) values were calculated. In addition, allele-specific polymerase chain reaction (PCR; Yaegashi et al. 2020) was used to detect the Y133F substitution on all isolates. Allele-specific PCR confirmed that approximately 80% of all isolates had the Y133F substitution. The culture medium tests showed that the EC₅₀ values were higher for isolates with the Y133F substitution than those without this substitution. When the isolates were inoculated and sprayed with difenoconazole and fenarimol fungicides, the fungicides showed effects on the isolates without the Y133F substitution but not on those with the Y133F substitution. Thus, we found that DMI-resistant strains of V. inaequalis were present in Hokkaido.

In Hokkaido, QoI fungicides have been used for controlling apple diseases. The high-risk of resistant strains of Venturia inaequalis, which cause apple scab, is also well known. We investigated the sensitivity of isolates of V. inaequalis in Hokkaido to QoI fungicides. We conducted polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP)-based analysis (Fontaine et al., 2009) to detect the G143A mutation of mitochondrial cytochrome b in V. inaequalis. The PCR-RFLP results showed that approximately 85% of all samples contained this mutation. We also observed that isolates with this mutation grew on a medium that had been treated with a QoI fungicide. Thus, a high proportion of V. inaequalis strains present in Hokkaido were resistant to QoI fungicides. When the resistant isolates were inoculated and sprayed with a QoI fungicide, the fungicide did not have the desired control effect.

Leaf mold (pathogen: Passalora fulva) and Cercospora leaf mold (Pseudocercospora fuligena), fungal diseases of tomato leaves, have very similar symptoms, while the conidiophores are morphologically distinguished. Therefore, an accurate diagnosis requires observing the conidiophores with a biological microscope. This paper proposed an in-field diagnosis method of both diseases through microscopic observation of their conidiophores by a commercially available sperm observation kit (product name: Men’s Loupe, TENGA Healthcare Inc.) attached to the camera lens of a smartphone. Among the kit components, two types of oval magnetic sheets (“Loupe” with a 550× ball lens in the center and “Plate” with a hole in the edge) were used. The loupe was attached to a smartphone so that the ball lens’s center overlapped the camera lens’s center. Conidiophores were collected from diseased leaf with cellophane tape. The plate with the cellophane tape covering the hole was magnetically attached to the loupe. Conidiophores were observed launching a camera application on the smartphone. The above method had the same diagnosis accuracy for both diseases as a biological microscope.

Ripe rot of grape caused by Colletotrichum spp. including the Colletotrichum gloeosporioides species complex (CGSC) is one of the important diseases in grape production. We re-identified seven grape strains deposited as CGSC in the NARO Genebank, Japan, based on the phylogenetic analysis with six loci (rDNA-ITS region, glyceraldehyde-3-phosphate dehydrogenase, actin, β-tubulin, calmodulin, and glutamine synthetase genes).These strains were isolated from five prefectures, i.e., Hokkaido, Yamanashi, Shimane, Hiroshima, and Fukuoka. Phylogenetic analysis based on these six loci revealed that one, three and three strains belonged to Colletotrichum siamense, Colletotrichum aenigma, and Colletotrichum viniferum, respectively. Leaves of potted grape plants were inoculated with three representative strains of three species. All inoculated plants exhibited leaf blight symptoms. Colletotrichum siamense, C. aenigma, and C. viniferum have not been reported as grape ripe rot pathogens in Japan, therefore; we propose these three species as the pathogens of the disease.

We evaluated the potential availability of the predictive model of pecky rice damage by Stenotus rubrovittatus using land-use data (Tabuchi et al., 2022) in Miyagi Prefecture, considering the data from the Miyagi Prefectural Plant Protection Office. We also improved the model from the combined data of the current study of 38 rice paddies from 2017 to 2020 and from previous studies. We then applied the current study data to the predictive model and calculated the predicted value of pecky rice damage. Moreover, the model of the previous study was improved by adjusting the parameter coefficients of the fixed factors. The accuracy of the improved model was evaluated by comparing the observed and predicted values of the model. The relationship between predicted and observed values was positive and marginally significant in the model of the previous study with the data of the current study. At the same time, the relationship was statistically significant in the improved model. The coefficient of determination of the improved model increased by 0.269 compared with the model from the previous study. Our study demonstrated that the predictive model of pecky rice damage was available with scattered data on the prefectural scale and was possibly applicable in other areas.