The effectiveness of three resistant potato varieties (“Tunika”, “Skutella, ” and “Maris Piper”) and three kinds of non -host crops (wheat, sugar-beet, and azuki-beans) in controlling the pathotype Ro 1 of G. rostochiensis was studied in a greenhouse. Five separate experiments were conducted with 1/5, 000 a pots. The population of the encysted larvae and eggs was decreased by 32-56% after being cropped once or twice with the non-host crops and by 66-93% with the nematode-resistant potato varieties. It was also decreased by 28-58% in the fallow soil. No noticeable difference was found among each of these crops or potato varieties in the effectiveness. It was learned that the combination of these non-host crops and nematoderesistant potato varieties in a rotation system would be effective to control this species of nematodes.

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The stimulative effect on the hatching of the potato cyst nematode, Globodera rostochiensis, was obvious already in the soil leachate collected from the soil around the rooting seed-tubers (hatching ratio: 52%), and it was high all through the growing season from germination of the seed-tubers to just after harvest (hatching ratio: above 90%). The soil leachate of sugar-beets gave low hatching ratios from beginning to end. The leachate taken from the soil where potato plants were grown in the previous year showed a higher effect on the hatching than that of non-host crops. This indicated the existence of residual hatching stimulant of potato plants in the soil over the year. Several potato varieties resistant to this species of nematode showed almost equaly high level of the hatching stimulative effect in comparison with susceptible ones.

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For estimating Heterodera cyst population in soils, the following four methods were compared: 1. cyst floatation with Fenwick's can, 2. centrifugal floatation of the float obtained by the former method, 3. decantation of undried soil into an 80 mesh sieve, and centrifugal floatation of the remainder on the sieve, 4. the same as the third method except for using air-dried soil instead of undried soil. The soils used in the present tests were volcanic ash loam from fields infested with the upland rice cyst nematode, Heterodera elachista, and soil previously added with the cysts. Results obtained were as follows:(1) significantly higher recovery rates and lower coefficients of variability were obtained by the 2nd and the 4th method, particularly the highest rate by the latter.(2) Using hypo (sodium thiosulfate) solution (s. g. 1.40) resulted in a higher recovery rate than with tap water or sugar solution (s. g. 1.20) for the centrifugal floatation technique.(3) It is concluded that examination of supernatant obtained by centrifugal floatation with hypo solution after decantation of air-dried soil appears sufficient to secure 90% recovery, and is practical as a simple, rapid, and inexpensive technique for estimation of the cyst population.

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Bursaphelencus lignicolus, which had been reared on Botrytis cinerea monoxenically in test tube, could be maintained at high population level at room temperature or low temperature (10-14°C) for long period of time by pouring sterile liquid paraffin into the tube, and did not lose its reproductivity and pathogenicity to pine tree by storage under the conditions for one year. The nematode reproduced on the fungus under liquid paraffin at 25°C.

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The gonad development of the pine wood nematode, Bursaphelenchus lignicolus, took the same pattern as Seinura spp., monodelphic nematodes; the posterior cap cell of genital primordium elongated without the separation of two large cells by somatic cells. The gonad of dispersal forms was suppressed compared with that of propagative ones; the gonad length of dispersal L_III was average 20μm, being about 2/5 of the propagative L₃'s, indicating the little development after the 2nd molt. The dispersal L_IV's gonad was about 67μm and 50μm in female and male, being about 1/2 of L₄'s respectively. The cloacal primordium was initiated in 3rd stage male regardless of the forms.

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Four amphimictic populations originating from geographically isolated localities including a crossing hybrid between the Mizuho and the Hawaii, and four parthenogenetics were separately multiplied and maintained on Norin 2 Ipomoea batatas La. in the glass house (15 to 34°C) for more than two years before tested. Development, reproduction and sex ratio of these populations on Fukuju 2 Lycopersicon esculentum Mill. in 5cm (i. d.) clay pot with steam-sterilized 2: 1 mixture of sandy loam soil and sand at different soil temperatures ranging from 15 to 33.4°C were examined by extracting nematodes from pot soils at intervals. All the amphimictic populations, more strikingly the Texas and M × H hybrid, showed a trend to develop faster than the parthenogenetics at most temperatures tested. More stimulated development expressed as the shorter life cycle (15 to 18 days) in the three amphimictics at high temperature (33°C) was clearly a contrast to the apparent retardation ofthe larval emergence and failure of the completion of life cycle in all the parthenogenetics at the same temperature. The primarily higher equilibrium levels of population densities per pot (about 75 ml of soil) in the amphimictics were 16, 000 to 18, 000 for the Mizuho, Hawaii and Texas, and 32, 000 for the M × H hybrid at temperatures of 20 to 23°C, and the secondarily higher levels were attained at about 30°C for each of the amphimictics as compared with the maximals of the parthenogenetics at 29.2°C; 23, 700, 23, 900, and 14, 300 for the Asahi-A, Asahi-B, and Shibi, respectively. The Akune (parthenogenetic) had the level of 6, 000 nematodes at 19.9°C, higher than that at 29.8°C. Both the temperatures of about 33°C and of about 16°C allowed the amphimictics to reproduce progeny to some extents, but did not the parthenogenetics. The maximal rates of reproduction (newly hatched, molting and developed nematode number per young female inoculated) were demonstrated to be 83.2 for the M × H hybrid and 31 to 51 for the other amphimictics at 20 to 23°C, while they were 17 to 30 for the parthenogenetics except for the Akune at 29.2°C. Sex ratio was not affected by soil temperatures; the amphimictics had approximate 1:1 of sexes or occasionally larger number of males regardless of temperatures, while the parthenogenetics bore no emergence of males, or very a few in the Asahi-A and -B. The basal temperatures for development of the amphimictics were 12.3, 11.6, 11.0 and 9.6°C for the Mizuho, Hawaii, Texas, and M × H hybrid, respectively, being lower than that of three parthenogenetics, 13.8, 13.4 and 14.4 for the Shibi, Asahi-A and -B, respectively. The Akune exhibited 10.5°C, but appearing more uncertain because of lack of the estimate for life cycle at the low temperature. The accumulated temperatures required for the completion of life cycle varied from 313.8 to 395.6 day degrees among populations. Differences were rather reasonably seen between the geographical populations than between the populations based on the reproductive mode.

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Egg-sacs of Meloidogyne incognita, hand-picked from the infected sweet potato roots in late summer (September)(E-S), and the second stage larvae, hatched within 48hr at 25°C from the egg-sacs (LE-S) or those recovered from the field soil in late summer (LS-S) and in midwinter (January)(LS-J), were stored in either water or soil at 0°C, then inoculated to garden balsams. The degree of infectivity was estimated by the numbers of root-knots produced on the plants. There was little difference in the infectivity between the inocula stored in water or in soil. After 5-day storage, average infectivity indices were 0.3, 9, 13 and 57 for LE-S, E-S, LS-S and LS-J, respectively.
To examine their low-temperature adaptation, effects of some chilling pretreatment on the cold tolerance were investigated. After successive storage for varying periods at low temperatures (10, 5, and 3°C) their cold tolerance (survival at 0°C) were significantly increased. The highest infectivity attained after the chilling treatment was not significantly different among inocula pretreated in various ways, being the same level as the LS-J.
The experiment suggests that the cold tolerance of this nematode varies according to developmental stages and seasons, and both larvae and eggs may be able to adapt to survive under low temperatures in winter.

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Investigations were made on the relationships between the nematode fauna and the properties of soil in the two orchards “Yamato” and “Hiratsuka” that differed in soil type in Kanagawa prefecture: Yamato soil was humic andosol while Hiratsuka soil was dystric fluvisol according to the FAO system. Yamato soil was composed of seven horizons and Hiratsuka soil was composed of 5 horizons as far as around 100cm deep. Although the two soils differed in the nematode fauna as well as in the physical and chemical properties, the following relationships were observe in both soils. The population density of nematodes was considerably related to the air phase and the liquid phase of soils. When there was a horizon whose hardness exceeded 6kg/cm³ or so, the population density of nematodes decreased conspicuously from the horizon to the lower horizons.

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