Potato plants (“Benimaru”) grown in chloropicrin-treated soil in Wagner pots were inoculated with eggs and larvae of Heterodera rostochiensis. The green parts were cut off 72 days after inoculation. The tubers were harvested about 1 month later and examined under a dissection microscope. Considerable numbers of female and various stages of cysts were observed on or just beneath the surface of those tubers which had received a high level of the inoculum. Most nematodes were found at the eye part which involved primordial buds, and a few were on the smooth surface of the tubers.

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Occurrence of acute wilting of chrysanthemum after a heavy rainfall was previously reported by the first author. In order to clarify the cause of the wilting, experiments were conducted in 1972 and 1973. Chrysanthemums grown in the nematodeinfested or uninfested soils were submerged up to the soil surface for several days. All of the plants including those grown in the steam-sterilized or nematode-free soils were wilted within several days. Wilting of the plants in the nematode-infested soil occurred sooner and severer than those of the uninfested soils, and plant growth was also severely retarded. Fungus species belonging to 3 genera were isolated from the naturally wilted plants. Inoculation of plants with each fungus was made and found that none of them did cause the wilting or affect the plant growth. Brown discolouration of a whole root system was observed prior to the occurrence of the wilting. Plant symptoms of the wilting were similar to those observed in the field. From these results, it is concluded that occurrence of the wilting in the field is primarily due to excess-soil moisture, but this is hastened and enlarged by the nematode infestation. Effect of the nematodes on the growth of chrysanthemum was not only in the general retardation of the plant growth but also in the delay of flowering and occurrence of leaf interveinal chlorosis. Plants grown in the nematode-free soil contained much potassium than those grown in the nematode-infested soil.

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Investigation on the causal agent of wilting disease of chestnut-tree called “Tachigare” widely occurring in this area was conducted in 1969-1971 at Reinan Branch Station, Fukui Agricultural Experiment Station, Mihama, Fukui, Japan. A high population of Pseudhalenchus anchilisposomus Tarjan, 1958, was found in the diseased roots at six locations in the chestnut-growing area. Symptoms of the disease are characterized by the blackish or brownish discolouration of roots as well as acute defoliation and wilting of the tree. The disease occurred specifically on matured trees of 5 to 8 year-old. It was observed that the more advanced the disease, the more the nematodes were recovered comparing with those from healthy trees in which very few or none of the nematodes were found. Morphology of the nematode of adults and larvae was studied, and description being given coincided mostly with that reported by Tarjan (1958). The nematodes were reared by the mycelial culture of Botrytis cinerea or Sclerotinia sclerotiorum, and also by the steam-sterilized chestnut roots. Test on the thermal death point of the nematode resulted in at 55°C for 10 min. Inoculation test revealed that several nematodes penetrated the epidermis of the young rootlets.

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This paper is concerned with the tests conducted in 1970-1971, on the transmission of tomato ringspot virus (TomRSV) by Xiphinema americanum which has been collected from soil of narcissus at Chiba, Japan. Soils containing viruliferous nematodes were subjected to air drying in a greenhouse at 22-30°C for one week, and examined on the infectivity of the virus without success. Soils were maintaind at a temperature as low as 4-10°C during a period ranging from a half to 14 months. By this treatment, the virus transmissibility still remained even after 14 months, although the infected petunia leaf or the juice of the infected leaves maintained also under the similar conditions indicated no infectivity after 4 or 2 weeks storage, respectively. Viruliferous nematodes obtained by sieving soils around the TomRSV-infected petunia roots, were used for some tests, and resulted in the following. The transmission rate of TomRSV by adults or larvae, or by the different developmental stages of larvae of X. americanum showed no significant differences. A serial inoculation of healthy plants with the viruliferous nematodes every 3 days revealed that the virus transmission succeeded until the eighth plant which is the final inoculation in this test. Another population of X. americanum collected from soils around grapevine at Chiba or from soils around citrus at Kanagawa was also used, and proved a similarly high rate of transmission of TomRSV.

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Commercial resistant varieties of tomato, F1 hybrid from “Anahu”, were severely affected by Meloidogyne incognita in glass-house at Oami, Chiba, Japan in 1972 where these varieties had been successfully cultivated since 1966. This nematode population (0-Pop.) was compared in pots with another population of M. incognita collected at different locality in Chiba (G-Pop.), in the number of larvae penetrated of the roots, development of the larvae after invasion, and gall formation of susceptible and resistant varieties of tomato, tobacco, and sweet potato. Two populations indicated no differences on the number of the 2nd-stage larvae penetrated within 24 hrs. after inoculation of the varieties tested of three crops, except for sweet potato on which number of larvae of both populations penetrated of the resistant varieties was significantly reduced than those of the susceptible varieties. Twenty days after inoculation were needed until egg-mass formation on susceptible sweet potato varieties for both populations, but 15 days on susceptible tomato or tobacco varieties. Gall formation of 0-Pop. on resistant varieties was as severe as those on susceptible ones of tomato, but galls were poorly formed on resistant varieties of tobacco and sweet potato. Poor galls were observed by the G-Pop. on resistant varieties of tomato, tobacco, and sweet potato. It is concluded that the O-Pop. is a strain of M. incognita which breaks resistance of tomato varieties of “Anahu”, and does not break resistance of tobacco and sweet potato varieties.

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In 1968, a resistant variety of sweet potato (Norin No.2) was found severely infested by a root-knot nematode originated from Miyazaki, Japan, in pots where this variety had been planted continuously for ten years. This nematode, keyed out to Meloidogyne incognita by the examination of the perineal pattern as well as host reaction test, was proved to be a new pathotype breaking resistance of another two sweet potato resistant varieties tested. As a preliminary trial, some physiological techniques were introduced to differentiate two pathotypes, resistance-breaking and ordinary one. No significant differences were indicated by the infrared absorption spectra of freeze-dried nematodes, and by the disk electrophoretic protein patterns of adult females, but the immuno-diffusion technique appeared to be promising for the purpose.

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Two 80-year-old citrus orchards, located at Yohchi and Issinden in Mie, Japan, were used for the experiments. These orchards were situated on a sloped land, and had a replant failure of citrus. Six experiment plots, 1×3m each, were set up in each orchard where Crossonema civellae, Pratylenchus loosi, and Tylenchulus semipenetrans were predominantly infesting. Treatment of soils at a half of each plot with 80% DBCP emulsifiable concentrate at 6ml/m² was made in April, 1970, and two-year-old Citrus unshiu plants grafted onto Poncirus trifoliata stocks were transplanted at 30cm intervals two weeks after treatment. Examination revealed that DBCP treatment significantly reduced nematode populations in both orchards, and this effect still remained to some extent in January, 1974 when the final examination was made. Treatment appeared to be phytotoxic, and growth of the replanted citrus was reduced in both orchards during the first two years, but in the third year the plants recovered their vigour and showed better growth than that of the untreated plots, although most plants situated at the lower part of the land at Issinden suffered severe damage from cold during the second winter. Correlation between the final nematode population and the weight of the above-ground part of citrus was evident at Yohchi. Necrosis of the feeder roots caused by Pratylenchus severly occurred in the untreated plots, and some incidence of the disease on roots was observed in both plots.

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Crossonema (Seriespinula) octozonale n. sp. was described based on the specimens collected from soil around roots of Japanese cedar (Cryptomeria japonica D. Don) at Fukushima, Japan. This species is characterized by eight longitudinal bands of spines, a comparatively long and slender stylet (97-112μ), 55-58 total annules, and the head annules which consist of two, set off from the body; the first annule with smooth margin and wider than the finely crenated second annule. This species differs from all of the described species in the subgenus in having smaller number of the longitudinal bands of spines. Jap. J. Nematol. 4: 47-50(1974)

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Morphology of a cyst-forming species attacking roots of upland rice in Japan which had been referred to Heterodera oryzae Luc et Brizuela, 1961, was studied, and Heterodera elachista n. sp. was described. This species is most closely related to H. salixophila Kirjanova, 1969, but can be differentiated from the latter by shorter stylet of adult female as well as the second-stage larva. This species also resembles to H. oryzae, H. sacchari Luc et Merny, 1963 and H. leuceilyma Di Edwardo et Perry, 1964, in the second stage larvae bearing 3 lateral lines, but differs from these species in possessing the thin underbridge without finger-like projections of cyst cone.

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[in Japanese]

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