ANNUAL REPORT OF THE SOCIETY OF PLANT PROTECTION OF NORTH JAPAN

A previously undescribed disease was observed on red and variegated heading types (radicchio) of chicory, Cichorium intybus L., in Iwate Prefecture in July, 2001. The pathogenicity of the fungal isolates obtained from the diseased plants was demonstrated. These isolates were identified as Rhizoctonia solani Kuhn AG-1 IB, on the basis of morphological and culture characteristics, an anastomosis test and PCR. This is the first report of bottom rot of chicory in Japan.

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A study was conducted to analyze genetic variations among subgroups within AG-2 and in AG-1 through AG-5 of Rhizoctonia solani using inter-simple sequence repeat polymerase chain reaction (ISSRPCR) fingerprinting. Of 14 microsatellite primers tested, five amplified PCR products. When 35 isolates were analyzed by ISSR-PCR fingerprinting with the primer (ACG) ₅, unique banding patterns were observed in AG-2-2 IV, suggesting that this method is useful for the preliminary discrimination of this group from other AGs for studying the population biology of the root/foliar rot fungus R. solani in sugar beet fields.

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The powdery mildew fungus on delphinium (cv.'Völkerfrieden', belladonna type) was identified as Erysiphe aquilegiae DC. var. ranunculi on the basis of morphological characteristics. Powdery mildew initially occurred in early June, 2004, under field conditions, and developed rapidly from late June to early July in delphinium growing in Aomori Prefecture. The average, maximum and minimum temperatures during this period were 20°C, 29°C and 10°C, respectively. Conidia of E. aquilegiae germinated at 5-30°C. The optimum temperature for germination in vitro was approximately 20-25°C. We suggest that the powdery mildew epidemic was related to field temperature. Cleistothecia initially formed on leaves in late June and gradually matured in late July in the field.

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To improve the method of assessing foxglove aphid (Aulacorthum solani) population density, the effect of sample units on the number of aphids was evaluated in the summer of 2004 in two soybean fields in Morioka City, Japan. There were some disparities in the number of aphids among sample leaves, and there are some indications of the improvement regarding the assessment method. First, more aphids were observed on the middle leaflet than on the right and left leaflets of a fully expanded trifoliate leaf; therefore, a trifoliate leaf should be appropriate as a sample unit. Second, more aphids were observed under the leaves that show many yellow spots on the upper side than under those with few yellow spots caused by aphid feeding; therefore, sample leaves should be chosen without predetermining the number of yellow spots. Third, many aphids were observed at the middle part of the plant in late summer and at the upper part in early autumn; therefore, sample leaves from each part should not be mixed. Fourth, significant differences in aphid population density between fields that differed in insecticide treatment were observed when 30 trifoliate leaves were sampled; therefore, 30 trifoliate leaves are likely to be sufficient for the detection of aphid population density differences among fields. Last, there were no significant relationships between adult number and nymph number on the same leaf when aphid population density was not very high, suggesting that adult aphids move frequently among soybean leaves, plants and fields; therefore, adults and nymphs should be counted separately.

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