The potato cyst nematode, Heterodera rostochiensis Wollenweber, has been identified for the first time in Japan from potato fields at Makkari, Hokkaido during July 1972. Population levels of the nematode in these fields appeared comparatively high. The nematode-infesting potato plants showed poor growth of the above-ground parts. General morphology of the larvae, adults, and cysts of this nematode is identical with one reported previously by other research workers.

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Sweet potato varieties of different susceptibility to Meloidogyne incognita were planted in pots to examine the larval invasion of roots and the rate of development. No varieties tested were found in which the larvae failed to invade. The development rate of the invaded larvae as well as numbers of egg-sacs counted on the unit length of roots were distinctively higher in the heavily galled varieties than in the slightly galled ones. Population levels of larvae in soils from both the resistant variety “Norin No.5” and the susceptible variety “Kanto No.14” were also examined throughout one year at approximately each 10th day, with the Baermann funnel technique. A higher population was shown by susceptible varieies than resistant varieties in which only very few larvae were detected.

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Survey of plant-parasitic nematodes associated with mulberry roots was conducted on 18 mulberry mosaic virus-infected mulberry fields and 130 uninfected fields in Gunma Prefecture. The genera found in the fields were Meloidogyne, Cryphodera, Helicotylenchus, Criconema, Paratylenchus, Xiphinema, Trichodorus, and Longidorus. Among these, Paratylenchus, Criconema, Xiphinema, and Trichodorus were found most frequently, and Paratylenchus and Criconema were at high densities. Meloidogyne and Longidorus were abundant in fields of alluvial soil, and Helicotylenchus was found more frequently in volcanic ash soil. Longidorus martini was found at a high rate in fields infected with the mulberry mosaic virus. Transmission of the virus by this nematode was proved by an inoculation experiment.

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Nematode survey was made with forest soil at eight locations in Kyushu, southwestern Japan. Soil samples were collected from forests of Pinus densiflora, Quercus acutissima etc. commonly associated with bamboo grass, and from recently reclaimed fields in the forest. Nematodes were extracted by the Baermann funnel technique. Among plant-parasitic nematodes isolated, Paratylencnus was found most frequently, followed by Hel icotylenchus, Trichodorus, and Meloidogyne. Xiphinema and Criconemoides were also obtained, but no specimen of Pratylenchus was detected in this survey.

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Nematode invasion of newly reclaimed fields by Pratylenchus coffeae was studied at seven locations in Nagasaki Prefecture where the occurrence of P. coffeae in fields, and the appearance of potato plant symptoms by infection of this nematode were examined. From these results, and the history of cropping recorded in these fields since the beginning, it is considered that P. coffeae may occur within six years or less after reclamation in some cases Rotting of potato tubers caused by this nematode may appear within ten years.

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Experiment on chemical and cultural control of the rice cyst nematode was conducted in a field which had indicated typical soil-sickness due to successive cropping of upland rice. Preplant treatment with D-D mixture at 30 l/10 ares was most effective and increased a yield of paddy rice variety by about 30%. This effect was not obvious in the next season, resulting from a rapid build-up of the cyst population at harvest time in the first year. Similar treatment with EDB (30%) was not as effective as D-D, and a higher cyst population was recovered. Treatment with Lannate (methomyl) 5 % granules at sowing time at a rate of 30 kg/10 ares was severely phytotoxic in combination with DCPA herbicide application which was made about one month after sowing. Another experiment indicated that cropping of soybeans or sweet potatoes decreased the cyst population remarkably at the end of the first season, but even 3-years successive cultivation of these non-hosts failed to decrease the population to zero. Rice yields of plots where a 3-year successive cultivation of soybeans or sweet potatoes had been made, was as good as 3.7 or 2.8 times that of the plots where rice had been successively cultivated for at least more than four years. Hatching stimulation of a water extract of rice roots to eggs of the cyst nematodes was apparent at 25°C under laboratory condition. Similar stimulation of kidney beans or sweet potato roots to this nematode was less and inhibitive at some concentration.

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The populations of Tylenchulus semipenetrans, Pratylenchus loosi, Criconema sp., Xiphinema spp., and Paratylenchus sp. were surveyed in a citrus orchard in Matsusaka, Japan, where the replant problem of Citrus unshiu Marcov. grafting on stocks of Poncirus trifoliata Rafin. has been known. Two 40-year-old trees exhibiting a slight decline were selected, and five cores of 100mf soil including rootlets were collected from each tree at monthly intervals from April in 1970 to the following April. Nematodes were extracted from each soil sample by sieving and double-layer centrifugal-floatation techniques. The population of Criconema sp. was highest throughout the year fluctuating between 400 and 4800 in one tree, and between 2200 and 12600 in another. The population of adults fluctuated to a lesser extent, compared with those of eggs or larvae decreasing in the late summer and early autumn. No significant difference in the population of five other species was observed between the two trees. The population in soil ranged from 10 to 1000 for T. semipenetrans, from 0 to 300 for P. loosi, and was less than 10 for Xiphinema spp. and Paratylenchus sp. P. loosi decreased in soil during the period from April to July, being in contrast to higher density in root tissues. T. semipenetrans in soil showed two peaks, spring and autumn, but did not fluctuate so highly in roots. Necrosis was observed on lateral feeder roots of a severe decline citrus.

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Inoculation experiments were conducted to confirm results obtained by Kiyohara and Tokushige in relationship to Bursaphelenchus lignicolus capable of causing wilting, or the death of pine trees. Twenty-three healthy trees of 7-year-old Pinus thunbergii and 10 of 12-15-yearold P. densiflora were inoculated on July 5, 1971, by the insertion of a water-suspension of the nematode into hole made on the stem, or on a branch cross section. Disease symptoms appeared first as a marked reduction in the oleoresin yield within 14 days after inoculation. At 50 days after inoculation, most trees, some of which had died, showed symptoms of wilting, yellowing, and browning of foliage. Transpiration of the leaves was measured at weekly intervals, and reduction appeared 22 days after inoculation. In an infected tree, it is considered that changes of tree physiology resulting in the reduction of transpiration occurs at an early stage of disease development. Population of B. lignicolus in wood tissue increased as the disease became more advanced. A large number of nematodes was found in various parts of a tree when symptoms became noticeable.

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