A regression model was developed for estimating yield loss of rice by panicle blast disease based on field experiments in 1991 and 1992. The model is y=0.764x+0.562, where y and x are the percentage of yield loss and that of affected panicles, respectively. This showed that apparent yield loss should not occur when less than 5 percent panicles were affected by the disease. Thus, this level is practically proposed as the yield loss threshold in Hokkaido.

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The pool-nursery is a new method to grow rice seedlings: after seeding and subsequent greening, nursery boxes are submerged in a tray of water so that the soil surface is 1-3 cm below the water until transplanting. We showed that this method suppressed the occurrences of both bacterial seedling rot and bacterial seedling blight at air temperature ranging from 25 to 35°C. The effect was the most significant at 35°C, at which these bacterial diseases would occur severely in conventional nurseries. To obtain a practical control level, the nursery boxes have to be submerged earlier than 3 days after emergence. Although diseases incidence were suppressed between 1-5% in the pool nursery, the pathogens were detected from seedlings with no symptoms when cultured on selective media. Further studies on the behavior of these bacteria are required if the pool nursery method is to be applyed as a component of a cultural control measure against the bacterial diseases mentioned above.

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Rice black-streaked dwarf transmitted by the small brown planthopper, Laodelphax striatellus, has widely distributed in the Kamikawa district of Hokkaido. However, the percentages of diseased plants were generally low. The occurrence of the maize streaked dwarf was also recognized in Higashikagura town. From seasonal flactuation of rice black-streaked dwarf in paddy fields, it was considered that the overwintering generation adults and the 1st generation larvae played the important role to the virus infection. The rice plant was susceptible to the virus until the 11th leaf stage. In the infected plant, the plant height was lower and the number of tillers increased as compared with the uninfected plant.

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To investigate reactions of potato cultivars in Japan to potato spindle tuber viroid (PSTVd), PSTVd was inoculated to seven potato cultivars. All cultivars inoculated showed some symptoms, but the severity of symptoms on both leaves and tubers were different among the seven cultivars. The cultivars Hokkaikogane, Norin No.1 and Danshaku-imo developed relatively severer symptoms than the other cultivars Waseshiro, Konahubuki, Mayqueen and Astarte. PSTVd in these plant leaves and tubers were detected by dot blot hybridization using digoxigenin (DIG) labeled cDNA probe. PSTVd accumulation did not differ among cultivars significantly. The result indicated that all cultivars were susceptible to PSTVd and this hybridization method was applicable to diagnose PSTVd in potato leaves and tubers directly.

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Five viruses, designated MB3, MB4, MB5, MB7 and MB8, were isolated from broad bean plants (Vicia faba) showing mosaic and/or necrosis in Miyagi Prefecture. MB3 and MB4 caused lethal necrotic symptoms on broad bean plants, whereas MB5, MB7 and MB8 usually caused mosaic, sometimes necrotic symptoms, but not lethal. Based on their host ranges, particle morphology, characterization of capsid proteins and genomic RNAs and serological properties, MB5, MB7 and MB8 were identified as a strain of bean yellow mosaic virus (BYMV), broad bean wilt virus (BBWV), cucumber mosaic virus (CMV), respectively. MB3 and MB4, formerly identified as necrotic strains of BYMV, were reidentified as a strain of clover yellow vein virus (CIYVV) and BYMV, respectively.

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The rapid progress of foliar symptoms with Cylindrocladium root rot disease of broad bean were closely related to the growth stage of host plant, but not to the change of weather conditions nor the length of period for growing in an infected soil. The root symptoms had previously and gradualy progressed one month before expression of the foliar symptoms which were progressed rapidly in the seed developing stage, followed by yellowing and falling of leaves. In the healthy broad beans, the root activity measured by using triphenyl-tetrazoliumchloride (TTC) method decreased in the seed developing stage. These results suggest some relationships between the reduction of root activity and the rapid progress of foliarsymptoms in the seed developing stage.

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In 1993, isolates of Fusarium oxysporum f. sp. melonis from diseased netted melon, Cucumis melo L., occurred at Hokuryu in Hokkaido Japan were identified as race2, according to Risser's system

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In 1993-1996, isolates of Fusarium oxysporum f. sp. melonis from diseased netted melon with yellows symptom collected at Yuubari, Numata, Kuriyama, Furano and Nakafurano in Hokkaido were identified as race 1, 2y, according to Risser's system.

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Cucumber mosaic cucumovirus satellite RNAs from melon were efficiently detected by microplate hybridization method using digoxigenin (DIG) labelled complementary RNA probe for satellite RNA. Satellite RNAs were quantitatively estimated using microplate reader like ELISA system.

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In summer in 1996, lesions and rotting with brownish black occurred on roots of carrot (Daucus carota L.) grown in fields at Hakodate, Hokkaido. Causal fungus of this disease was identified as Fusarium solani (Martius) Saccardo f.sp. radicicola (Wollenweber) Snyder et Hansen from the pathogenicity and the morphological characteristics.

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Undescribed diseases of leek (Allium porrum L.) and garlic (Allium sativum L.) have occurred in Miyagi Prefecture from 1993 and 1995, respectively. In both crops, leaves and sheaths were mainly affected, and the symptoms were elliptical brown to purple lesions, becoming zonate with the developing of the causal fungi on lesions. Pathogenicity to each host plant was demonstrated by the inoculation of isolates from both diseased plants, and the isolates were identified as Alternaria porri (Ellis) Ciferri on the basis of morphological and cultural characteristics. This is the first report on purple blotch of leek and garlic in Japan.

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In 1992, stunting and early flowering occurred in chrysanthemums cultivated in Naganuma, Yubarigun, Hokkaido. Chrysanthemum stunt viroid was detected from these plants by polyacrylamide gel electrophoresis (PAGE) and hybridizaion using digoxigenin (DIG)-labeled cDNA probe prepared from full-length cDNA clone of CSVd in Tochigi Prefecture. CSVd isolated from cv. Popular in Tochigi Prefecture consists of 354 nucleotides and shares 98 % identity to CSVd-English isolate and 97 identity to CSVd-Australian isolate in overall nucleotide sequence. Dot blot hybridization using DIGlabeled cDNA probe specifically detected CSVd in 2M LiCI-soluble nucleic acids corresponding to 171ig of fresh leaf weight, which gave a sensitivity of detection at least 100-times higher than return-PAGE, and considered as a suitable method for practical diagnosis of CSVd in cultivated chrysanthemum plants.

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In 1996, a fungus was isolated from leaf spots of carnation (Dianthus caryophyllus L.) cv. Wink collected from six plastic-film houses of three farms in Nanae-cho, Hokkaido. The fungus formed many conidia on the colony, cultured on PSA medium at 20°C under conditions of the Black Light Blue light. Typical lesions observed in the field were formed on the leaves of carnation by spraying of the conidia and the pathogen was reisolated from the lesions. The conidia were dark brown, straight or slightly curved, measuring 28-48×8-12μm, typically 2 or 3 celled cylindrical. The cell wall of the conidia was rough, echinulate to verrucose. Causal fungus of this disease was identified as Heterosporium echinulatum (Berkeley) Cooke from the pathogenicity test and the morphological characteristics of the conidia. The optimum temperature for growth of the fungus in culture was 20°C and for infection, 15°C.

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Fourteen fungicides were tested by natural infection and conidial inoculation of the pathogen for control of leaf spot disease caused by Heterosporium echinulatum in carnation variety Light Pink Barbara in a plastic-film house. Among these, two fungicides (tetraconazole and fluazinam) were more effective for the control.

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In 1996, a disease indicated as rhizome rot was detected on German iris in Hokkaido district. During storage infected rhizomes underwent progressive decay at a slow late. Botrytis isolates collected from diseased rhizomes were pathogenic to rhizomes of German irises. Sclerotia on a PDA culture were characteristically shiny black and convoluted agglomeration. Conidia were ovoid to ellipsoid, hyaline, 8.2-18.5×5.1-11.1μm in size. Surface structures of Conidia were found to be hairy from scanning electron microscope observation. Thus, the fungus causing the disease was identified as Botrytis convoluta Whetzel et Drayton. This is the first report of Botrytis rhizome rot of German iris in Hokkaido.

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The isolates of Valsa ceratosperma from some broad leaf trees including apple trees were inoculated to dormant apple branches. While the isolates from apple trees were highly pathogenic to the apple branches, the isolates from broad leaf trees except apple trees had no pathogenicity to them. As these isolates were grown on liquid medium added phloridzin, the isolates from apple trees degraded phloridzin quickly, but the isolates from broad leaf trees except apple trees did not degrade it.

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The Japanese pear spray calendar was recognized as an effective control method of pear diseases on cv.‘La France’ and ‘Le Lectier’ with the ambient temperature ripening but not with constant 20°C temperature ripening. The apple spray calendar was also effective to control diseases on ‘La France’ with both the ambient and constant 20°C temperature ripenings. In the case of ‘Le Lectir’, this is effective only with ambient temperature ripening.

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Reproduction probability and source populations of Sogatella furcifera in Akita Prefecture were studied from 1981 to 1996 with 43 population monitoring paddy fields wherein no insecticide was applied. The probability for adult to produce the next generation was as high as 100% during early rice growth stage, and declined since 20 days before appearing 50% neck-node of rice plant (NA₅₀) to 23 days after NA₅₀. Fifty percent probability was estimated to apear 9 days before NA₅₀ in coastal area and 5 days after NA₅₀ in inland area. The source populations were originated with 81% immigrant, 5% reproduced, and 14% mixtures in coastal area and 63%, 2%, and 35% in inland area, respectively.

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The larvae of a chironomid fly, Smittia akanduodecima Sasa et Kamimura, were found to injure seedlings of Adzuki bean and Kidney bean before the sprout in Hokkaido. The larvae attacked primary leaves of beans, not cotyledon as in the case of seed corn maggot. In Adzuki bean, the damage was so severe that the seedlings hardly grew. These injuries occurred in marshy soil especially when plowed with beet tops in spring. It appears that the odor of fermentation may have attracted the females to oviposite eggs, and the delay of bean sprout caused by low temperature may have resulted in lengthened susceptible period.
The chironomids caused seedlings injury over 2000 ha of legume crops in Tokachi district in 1967 were identified to Smittia aterrima (Meigen) and S. nudipennis (Goetghebuer) based on voucher specimens.

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