Reactions of 44 species including 58 strains of Nicotiana to the root-knot nematode, Meloidogyne javanica, were examined by inoculation of the seedlings with the larvae under 27°C in a temperature tank. Using the five developmental classes ranging from larvae to egg-laying females, the each number of the parasites in the all roots was recorded at 23 days after the inoculation. According to the average number of the nematode in each developmental classes, these species were divided into following three groups. 1) High resistant group: the parasites were not observed in the roots or a few parasites remained in the larval stage of class A. Nicotiana nudicaulis No.1, N. plumbaginifolia No.1, No.2 and No.3, and N. repanda No.1 and No.2 were included in this group. 2) Moderate resistant grou: the retardation of parasite development was similar to that of N. tabacum cv. RK 70 and more than seventy percent of infected parasites remained in the larval stages of class A and B. N. affinis (Hort.) No.3 and No.4, N. exigua No.4, N. knightiana No.1, N. megalosiphon No.3, N. otophora No.1 and No.2, N. paniculata No.2 and No.3, and N. suaveolens No.2 and No.3 were included in this group. 3) Susceptible group: the roots had many large galls and a great number of parasites were developed to the mature female stages. The other species, not mentioned above, were included in this group.

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The fecundity and adult life span of Bursaphelenchus lignicolus were studied at 25°C by transferring the same females and males at intervals to new fungus cultures of Botrytis cinerea until they died. B. lignicolus laid an average 79 eggs per female over a 28-day oviposition period. The maximum number of eggs laid by a female was 216. Peak oviposition generally occurred within 4 days after egg-laying commenced and averaged 5.5 eggs per day during the time. Thereafter the number of eggs laid declined. Adult females died shortly after oviposition ceased. The rather high mortality of adults was observed. The average adult life span of female was 15 days, and the maximum was 32 days. The net reproductive rate per generation R_o was derived from the age-specific fecundity rate m_x and the female survival rate l_x. Then intrinsic rate of natural increase r (=0.832) was calculated from R_o, thus logN_t/N_o=0.832t give a theoretical curve of population increase of B. lignicolus in an unlimited environment. Jap. J. Nematol. 7: 6-9 (1977).

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Single egg mass of the root-knot nematode (Meloidogyne incognita) was collected from three districts in which different crops were cultivated. Each population, reproduced on a susceptible variety of tomato for three or four generations, was inoculated to resistant and susceptible varieties of tomato, sweet potato and tobacco at different temperatures (25 to 33°C). Root-knot index of two populations on three crops was higher on the susceptible varieties than the resistant ones at these temperatures, and it was raised by higher temperature. The Oami population, however, indicated a high root-knot index only on resistant variety of tomato as well as on a susceptible one. Reaction on other crops was similar to the other two populations. The parasitic ability to resistant variety in successive generations of which reproduced on resistant variety at higher temperature rose apparently in Genshu population to tomato and in Kaijyo population to sweet potato. Finally parasitic ability to resistant variety of two populations developed as same as to susceptible one under lower temperature.

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Healthy seedlings of 54 species selected from 20 botanical families were grown for 8 weeks in pots with soil inhabiting L. martini which had been reared on MRSVinfected mulberry plants for 5-6 months. Among them fig, grapevine, tomato, eggplant, tobacco and petunia were the only plants recognized as the host of the nematode, but they were not infected at all with MRSV by the nematode transmission. On the other hand, another 11 plant species were systemically infected with the virus by a mechanical sap inoculation technique using MRSV-infected cowpea leaves as an inoculum, but all of these plants were non-host of the nematode. Thus, in this experiment, susceptible plants to the nematode transmitted MRSV were not recognized other than mulberry plant. Retention times of MRSV in L. martini, which maintained in host-free soil, differed with storage temperatures; 13 months, more than 18 months and 3 months under room temperature (0-28°C), 0-9°C and 20-24°C, respectively. Some nematodes could retain the active virus in their body as long as they were alive. Although no significant differences were observed in the virus transmission efficiencies between 2nd- or 3rd-stage larvae and adults of the nematode, the transmission by newly hatched 1st-stage larvae was not recognized. Healthy seedlings of mulberry plant were perfectly infected with the virus even when only single viruliferous nematode was associated with roots for 7 or 10 days.

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The behavior of Di-Trapex (20% methylisothiocyanate + 80% D-D) in a field has been studied. The chemical was applied in the Kuroboku soil (sandy clay loam). The soil sample was prepared from different times and different depth after fumigation. The concentration of fumigant were determined by means of gas chromatography. It was evident that methylisothiocyanate (MITC) and 1, 3-dichloropropene (1, 3-D, active ingredient of D-D) differed in the rate of release from soil. MITC exhibit the rapid disappearance curve from one week to three weeks after application, while 1, 3-D was detected at less than half amount of initial dose one week after application and then the gentle disappearance curve was observed. Finally, 7 weeks after application, the concentration of MITC and 1, 3-D in the soil reached to 0.5 ppm more or less respectively. Furthermore, the test was carried out to study the influence of aeration on the residues of compounds treated in soil. As the result of aeration conducted one week after application, no significant difference was observed in the rate of 1, 3-D disappearance. The release of MITC from soil was promoted by an aeration especially in the deeper layer (10-20 cm) when Di-Trapex was applied at 15 cm depth. No significant efficacy for aeration was obtained between plow and rotary cultivation.

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Propagation of Pratylenchus spp. on alfalfa callus tissues was compared with three modified nutrient media of Shenk & Hildebrandt's (SH), Khera & Zuckerman's (KZ), and Krusberg's (K) medium. Propagation of nematodes were not always correlated with the growth of callus tissues. Kinetine, p-chlorophenoxyacetic acid, inositol and ascorbic acid had effect on the propagation of P. coffeae; P. fallax, P. penetrans, and P. vulnus differing between SH medium and KZ medium. P. convallariae propagated better on K medium than on SH medium, while P. coffeae, P. loosi, and P. zea laid more eggs on the latter than the former. Disodium EDTA had no effect on the propagation of P. penetrans and P. vulnus on K medium. Ratio of egg to adult and larva of P. coffeae, P. loosi, and P. penetrans in number declined five months after inoculation on SH medium and K medium.

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A three-year survey was made to learn the seasonal occurrence of the potato cyst nematode, Globodera rostochiensis (Woll.) Mulvey & Stone, in a commercial potato field in Makkari Village, Hokkaido, Japan. Second stage larvae first appeared early in May and invaded into the potato roots as soon as they started growing. The number of nematodes within the roots reached a peak in the middle of June. Female adults were abundant on the roots during July and the cyst population increased in the soil following this period. Although the second stage larvae, which had decreased once in July after a peak in the middle of June, increased again in the soil in August, there was no appreciable indication of the occurrence of the second generation in the practical sense. Since no second stage larvae were isolated from the soil during March and April, it is considered that this nematode species does not overwinter as the form of second stage larvae free in the soil. Jap. J. Nematol. 7: 33-38 (1977)

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On the field strawberry plants, the strawberry bud nematodes, Nothotylenchus acris increased in number in spring, precipitiously decreased during warm and dry summer, rapidly recovered to the highest level in autumn, and maintained a low level throughout a cold winter. No nematodes were detected in the internodes of stolons during the reproductive season of the plants. The disseminating nematodes were already in the apical buds of runners still in the mother plants. During the seasons unfavourable for the reproduction and maintenance, the 4th stage larvae and female adults before full maturation were capable of survival. Nematodes in these developmental stages also survived in the dried strawberry buds for 410 days at 5°C. The resuscitation occurred after the freezing treatment at-20°C for 4 days. Satisfying recovery was gained when the buds were pre-dried at room temperature before the freezing treatment. Jap. J. Nematol. 7: 39-44 (1977)

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[in Japanese]

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The infective larvae entered the roots of rice plant in the middle of May. Adultfemale deposited eggs in the geratinous matrix after five weeks from penetration. Cyst formation was completed after six to eight weeks from entry. In larval population fluctuation four peaks were observed; it is considered that the first peak observed in the middle of June was that of larvae which emerged from cysts surviving the winter, the second one in July to August was derived from the first generation, the third one in the middle of August was from the second generation and the last one in the beginning of September was from the third generation. The first and the second peaks were higher than the later two ones. Cyst density gradually decreased from early April to late August, then it increased to the initial density at September except in fallow plot. The rates of empty eggs in cyst were very low in spring but it increased after sowing the rice. Developmental zero was 10.6°C and sum of effective temperature was 455 day-degrees centigrade for a completion of one generation. The adult female produced a large quantity of eggs in the egg mass. The time required to larval hatch was shorter in egg mass than in cyst and hatching rate was higher in egg mass than in cyst. Therefore, it is considered that larvae from egg masses chiefly infested during rice growing season, on the other hand, cysts surviving the winter played an important part in the propagation in the next spring. In generation-isolating experiments, three generations were observed in a rice-growing season. Vertical and horizontal distribution patterns of this nematode in soil were closely related to the root distribution. The population density of cysts was highest in the soil layer from surface to depth of 10 cm, and in the widths of 12.5 cm toward the right angle with row from the center of the hill.

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In lily fields in Kanto district and Niigata prefecture, Pratylenchus penetrans was exclusively dominant in almost all fields infested with root-lesion nematodes, but there were a few fields which were coinfested with P. vulnus. The nematode infection was extremely severe in roots of henry's lily and showy lily which were usually grown for several years from the infected small bulbs. On the other hand, it was generally light in roots of elegant lily and gold lily, the former was grown from a seed and the latter for only one year from a scarcely infected native bulb collected in forest land. In most fields of showy lily, population densities of the nematodes in roots and in soil had maximum in July or August. After November when lily bulbs were dug up, the population in soil was kept at rather low level. At that time, ratio of second-stage larvae increased. Among taro, maize, upland rice, peanut and sweet potato, cultivation of taro or peanut was effective for reducing population densities of the nematodes in fields. When small bulbs (ca. 5.2g each) of showy lily infected with the nematodes were treated with hot water, a treatment at 47°C for 45 min. was the best one which eradicated the nematodes without hindering growth of the lily.

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Observations were made on the fall crop of potato in 1975 in a field coinfested with Meloidogyne hapla and M. incognita. This crop was planted at the end of August. Mean soil temperature (-10cm) in the first half of September of this year was 28.8°C which was 3.3°C higher than that of the average year. Rate of the failed sprout of potato in three plots where root-knot index was 0 % by application of EDB (the following was in the same manner) was 13.1 to 20.5 %, whereas that in each plot of 75 % and 100 % of the index was 43.3 % and 49.5 %, respectively. Plant height measured as an index of the growth of potato in three plots where root-knot index was 0 % was 32.1 to 33.9 cm, whereas that in each plot of 75% and 100% of the index was 22.1 cm and 16.0 cm, respectively. Rate of the bacterial wilt in three plots where root-knot index was 0 % was 7.6 to 12.1 %, whereas that in each plot of 75% and 100% of the index was 21.7% and 27.4%, respectively. Yield per are in three plots where root-knot index was 0 % was 156 to 186 kg, whereas that in each plot of 75% and 100% of the index was 43 kg and 10 kg, respectively.

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The effects of excised root tips of some plants on larvae of the root-knot nematode, Meloidogyne incognita acrita, were investigated with the watch glass containing 0.5% water agar. It was found that every root tip of tested plants had a repellent effect on the nematode. The repellent effect had continued from one to three hours and then disappeared except tobacco root. The repellent substance seemed to be released from the cut surface of the root.

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Infestation of white tip nematode in paddy rice have lately increased in the greater part of Japan, and gradual permeation of newly developed mechanical transplanting rice culture have been considered as a possible cause of the increased infestation. In order to confirm this, some observations on the nematode populations were made in comparison between the mechanical transplanting (MT) culture and ordinary hand transplanting (HT) culture. In nursery bed for the MT culture, in which seeds are always sowed densely on a special medium in standardized plastic box and germinated under higher temperature condition than those of the ordinary cultures, the majority of the nematodes originated from the infected seeds reinvaded the young seedlings and active reproduction of the nematodes were observed. On the other hand, only a few nematodes reinvaded the ordinary beds for the HT culture. In field trials on dissemination of the nematodes from infected plants (inoculm) to healthy plants, the earlier inoculations were more effective than later ones for the nematode dissemination in both cultures, but the degrees of the dissemination were significantly higher in MT culture, in which more younger seedlings were used, than in HT culture. From these results, it could be concluded that the occurrence of the nematode would more severe in newly developed MT cult ure than ordinary cultures.

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