第26巻 第1/2号 日本線虫学会誌 1996年12月

Growth and Propagation of the Rice Stem , , on Rice Seedlings and Fungal Mat of Botrytis cinerea

Md. Rustom Au and Nobuyoshi ISHIBASHI*

Life cycle studies of Ditylenchus angustus demonstrated that one generation time

from egg to egg took 8 days on one-week-old rice seedling at 24-26•Ž. The eggs were

laid at 2-celled stage and embryos hatched in sterile water 64-66 hr after the egg-

laying. The duration of J2, J3 and J4 was 1,1 and 2 days, respectively. Females started

the egg-laying 1 day after the adulthood. Fecundity of D. angustus on rice plant was

always higher than on the fungus, Botrytis cinerea. Fecundity declined on both hosts

following the pre-culture on the fungi for 1 month (1MF) or for 6 months (6MF) prior

to inoculation. D. angustus increased 1067,993 and 734-fold on rice plant 40 days after

inoculation with 20 adults (10 females and 10 males) collected from rice plant, 1MF

and 6MF, respectively. On B. cinerea after the same period from the same initial

population the multiplications were 291 and 229-fold, from the inoculum from rice

plant and 6MF, respectively. Jpn. J. Nematol. 26 (1/2) 12-22 (1996). Key words: Ditylenchus angustus , rice stem nematode, life cycle, fecundity.

Ditylenchus angustus is an obligate and serious pest of rice plants causing "ufra" disease. Ufra was first reported by BUTLER (4) in 1913 from East Bengal in India, now Bangladesh. Ditylenchus angustus is generally called "rice stem nematode" due to its inhabiting the rice stem. They feed ectoparasitically on younger or soft leaves, leaf sheaths, peduncles and spikelets. As a result, the plants become stunted causing severe yield losses (3). The are usually spread by water. Ufra is mainly found in deep water rice fields, however, recently it is spreading in irrigated rice fields (2, 15, 17). Severe yield losses of 1.26 to 3.94 t/ha have been recorded with only 4 to 10% initial infected seedlings at the transplanting stage (18). An efficient management of this pest requires information about its life cycle. Recently, growth and reproductive parameters of this nematode have been investigated on fungal host, Botrytis cinerea (1). However, no reports are available about the detailed studies relating to the life cycle and reproduction on its original host rice plant. This paper reports the life cycle and reproduction of D. angustus on the rice plant in comparison with those on the fungus, B. cinerea.

MATERIALS AND METHODS

A pure culture of D. angustus was obtained from Bangladesh Rice Research Institute, Gazipur, Bangladesh, and was maintained in a glasshouse on a susceptible japonica rice cv. "Reiho" . Nematodes from infected plants were extracted by cutting the upper portion of the stem

Department of Applied Biological Sciences, Saga University, Saga 840, JAPAN. *To whom all correspondence should be addressed .

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(1 cm. apart). Active nematodes were hand-picked under a stereo microscope and checked by a compound binocular microscope for the establishment of two types of stock culture.

Culture on sterile rice seedlings: Ditylenchus angustus was monoxenecally cultured on nutrient medium in a petri dish by using the technique developed by PLOWRIBHT and AKEHURST (20) with a little modification. Briefly, two hulled rice seeds cv. Reiho were surface-sterilized with mercuric chloride (0.1% w/v) for 30 min and rinsed 5 times with sterile distilled water, then placed on GAMBORG's B-5 basal medium (10) supplemented with sucrose (2% w/v) in 9 cm diam. petri dishes with 1% agar. . The culture was maintained at 24-26•Ž with 12L: 12D photo period. Thirty days after sowing, the seedlings were inoculated with 30 adult nematodes surface-steril- ized with malachite green (0.1% w/v) for 15 min followed by rinse three times with sterile water.

The nematodes were directly pipetted with 15 ill water to a cotton mass wrapped the leaf base of the seedlings. The petri dishes were sealed immediately by polyvinyl chloride tape and returned to the same controlled environment.

Culture on the fungal mats of Botrytis cinerea: Botrytis cinerea was inoculated on an oblique substrate in a 18 cm long test tube containing 8 ml potato dextrose agar. Five days after the fungal inoculation, 40 adult nematodes which were surface-sterilized with mercuric chloride

(0.01% w/v) for 15 min followed by wash 5 times with sterile distilled water, were introduced to it by pipetting with 20 dal water. The test tubes were incubated at 24-26•Ž in the dark. After the population reached a maximum, the nematodes were subcultured up to 6 months by transferring old fungal mat with nematodes to a new mat. The nematodes multiplied on either sterile rice culture or on fungal mat were used as inocula for the following experiments.

1) Determination of life cycle on rice plant:

The inocula used for this experiment were freshly hatched 2nd stage juveniles (J2). To obtain J2 enough for experiment, a large number of eggs was collected from infected rice stems of pre-established sterile rice culture, washed 4 times with sterile distilled water and incubated at 24-26•Ž in a concaved glass slide. The hatched J2 were collected at 4-hr intervals and 15 J2 were inoculated on a one-week-old rice seedling (cv. Reiho). The petri dishes were sealed and incubated under the same condition. The nematodes were recovered at every 24 hr intervals and subjected to gentle heat killing for the record of body size and growth stage. The growth stages were determined on the basis of their body length (11). The investigation continued until the development to adulthood and the commencement of egg-laying. Five seedlings were harvested for each observation day.

To determine the time required for egg hatching, the newly laid 2-celled eggs were incubated in sterile water at 24-26•Ž and observed at regular intervals until hatching.

2) Fecundity of D. angustus on rice seedlings from different inoculum sources:

Adult nematodes for these experiments were collected from rice plant or fungal mat with two different periods; 1-month-culture on fungus (1MF) or 6-month-culture on fungus (6MF). From rice plants, the nematodes were collected from pre-established nematode population on rice seedlings within 25-30 days after inoculation. Active male and female adults were hand-picked and kept in sterile water under aseptic condition. Ten each of male and female adults with 10,al water were inoculated onto a 30-day old rice seedling growing on B-5 medium by pipetting to a cotton mass stuffed into a sheath crevice. The petri dishes were tightly sealed with polyvinyl chloride tape and returned to 24-26•Ž under 12L: 12D photo period.

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Similarly two separate experiments were conducted with the adults from the stock fungal cultures. of 1MF or 6MF. Active males and females were surface-sterilized in malachite green

solution (0.1% w/v) for 15 min and washed four times with sterile water. Ten each of male and female adults were inoculated to a 30-day old rice seedling growing on B-5 medium as mentioned

above. The petri dishes were sealed and incubated at 24-26•Ž under 12L: 12D photo period.

Nematodes were separately recovered from stem (leaf sheath) and leaf blade 10, 20, 30 and

40 days after inoculation. Nematodes on petri dish lid and on agar surface were carefully

collected and counted. Number of nematodes/g wet rice tissue was calculated. Ten replications were maintained for each treatment. From the initial and final population, some of the primary

characteristics such as average body dimensions of females or body colour density (lipids)

expressed as shade gradation were recorded. Measurement was made including eggs from each

distribution, and percentages of growth stages were calculated. Data were analyzed with analysis

of variance (ANOVA) and the means were compared by Duncan's multiple-range test (p=0.05).

3) Fecundity of D. angustus on B. cinerea:

Adult nematodes were collected from 6 months old B. cinerea culture (6MF). Ten each of male and female adults were introduced to 5 days old culture of B. cinerea growing on PDA medium (agar 1.5%) in test tubes (18 cm long) or in concaved slides (10 mm diam. 3 mm depth).

To prevent desiccation, the slides were kept in sealed petri dishes in which a moist filter paper was provided. The test tubes and the petri dishes were incubated at 24-26•Ž in the dark with 10 replicates for each batch.

In a separate experiment adult nematodes were collected from the sterile rice culture . Male and female ten each were inoculated to 5 days old B. cinerea culture growing in test tubes or concaved slides, being incubated in the same way as above mentioned . For each treatment 10 replications were maintained. Ten, 20, 30 and 40 days after inoculation, the nematodes were recovered by rinsing the test tubes or concaved slides with water. The remaining nematodes in the fungal mat or in the agar plate were carefully recovered under a stereo microscope. The nematodes recovered were counted and their stages were recorded.

RESULTS

Life cycle:

One generation time from egg to egg was 8 days on rice seedlings growing in vitro at 24-26•Ž

(Table 1). The half period of one generation, 4 days, was devoted to juvenile development: 1,

1 and 2 days for the 2nd, 3rd (J3) and 4th stage juveniles (J4), respectively . The average body length was 419 16 (S.D.),um for J2, 576•}38,um for J3, 720•}64,um for

J4, 795•}25,um for male adults, and 840•}15 pm for female adults. Therefore the three juvenile stages were determined by their non-overlapping body length. The body length of J4 and newly- formed adults were partly overlapped, but they were easily distinguished from each other by external gonad characteristic.

Female adults started oviposition 1 day after developing to adulthood. The deposited eggs were all at 2-celled stage, completed embryogenesis in 64-66 hr, and embryos reached to J2 hatched out spontaneously in sterile water.

Fecundity on rice:

The fecundity of D. angustus on rice plants is shown in Fig. 1 showing variable fecundity

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Table 1. Growth and development of Ditylenchus angustus on rice seedlings in petri dish after inoculation with the freshly hatched 2nd stage juveniles.

1) Each value is the mean of 20 individuals with standard errors. Body length of juveniles is a mixed value of males and females.

Fig. 1. Reproduction of Ditylenchus angustus on rice seedlings in petri dish afterinoculation with 10 each of male and female adults of the nematode obtained from three different sources: from rice plants (•›), from 1 month culture on Botrytis cinerea

(•œ) and from 6 months culture on B. cinerea(•¢). Vertical lines indicate standard errors.

depending on the inoculum source. The increase in reproduction on rice from rice, 1MF and 6MF on day 10, 20, 30, and 40 after inoculation were; 7.5, 210, 705 and 1067-fold, 5.5, 162, 624 and 993- fold, and 4.8, 142, 489 and 734-fold of the inoculum population, respectively. Thus the highest fecundity was obtained from rice plant, being followed by 1-month-fungus culture (1MF). The lowest fecundity was from 6-month-fungus culture (6MF). After inoculation, the rate of population increase was very slow until 10 days, thereafter the population rapidly increased, regardless of the inoculum sources. The reproduced numbers of nematodes subcultured from rice to rice plants were significantly higher than that from 6MF, whereas these nematodes from rice to rice plants were significantly higher only up to 20 days with that obtained from 1MF (p=0.05). The reproduced numbers of nematodes stemmed from 1MF and 6MF were not significantly different up to 30 days but they were significantly different on day 40 (p =0.05).

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A B

Fig. 2. Population structure of Ditylenchus angustus on rice seedlings in petri dish after inoculation with 10 each of male and female adults of the nematode obtained from rice plants (A) and from 6 months culture on Botrytis cinerea (B). Black column; 2nd stage juvenile, open column; 3rd stage juvenile, dotted column; 4th stage juvenile, stripped column; adults.

A B

Fig. 3. Distribution of Ditylenchus angustus on rice stem (0), on rice leaf blade (0), and not on rice seedlings (A) after inoculation with 10 each of male and female adults. The nematodes used as inoculum were obtained from rice plants (A) and from 6 months culture on Botrytis cinerea (B).

Fig. 2 shows population structure of developmental stages of D. angustus from different inoculum sources on rice. These stages of nematodes from rice to rice indicate that up to 20 days, J2 and J3 compose about 40% of total population, on day 30 they reduced to about 30% and on day 40 dropped to 7.5-12%. At the same time, the population of J4 and adults reached to about 83% of the total. Contrarily, J2 and J3 in the population originated from 6MF, occupied 40% of the total population up to 30 days after inoculation, and on day 40 it declined to 30%, whereas J4 and adults comprised to about 70%. From rice to rice, the accumulation of J4 and adults began 30 days after inoculation, while the accumulation of these stages began 40 days after inoculation from 6MF to rice. The distribution of nematodes on the rice plant took the same tendency either from rice to rice or from 6MF to rice up to 20 days (Fig. 3). On day 10, 95% of the total population were seen

―16― Vol.26No.1/2 Japanese Journal of Nematology 1)ecember,1996 in the stem and on day 20 about 50% in the stem, 45% in the leaf blade and only about 5% outside the plant, i. e., on the agar surface or on the petri dish lid. From 30 to 40 days, there was a reduction of population in the leaf blade and increase in the population outside the plant surface, which was higher (19.5%) in the inoculum from rice than that from 6MF to rice (13%). Table 2 shows the mean number of nematodes/g wet rice tissues form different inoculum sources. The largest number was obtained from rice to rice inoculation; 6,567/g followed by 1MF (6,188/g) and the smallest was from 6MF (4,818/g) 40 days after inoculation. Table 3 shows body dimension and body colour density (lipids) of the nematodes from different inoculum sources. The initial and final body dimension of the nematodes from rice to rice remained unchanged. The nematodes reduced their body length by 9% when they were continuously cultured on the fungal mat for 6 months. At the end of the culture, 40 days after inoculation, body contents of the nematodes on B. cinerea became transparent, whenthose from rice to rice kept comparatively dense colour. The nematodes cultured for 6 months on B. cinerea regained their original body length 40 days after being transferred to rice plant (Table 3). Fecundity on B. cinerea: The population development of D. angustus on the fungus B. cinerea from rice plantor 6MF is shown in Fig. 4. The increase in population was larger when the inocula were originated from

Table 2. Propagation of Ditylenchus angustus on rice seedlings in petri dish.

1) Nematodes used as inocula were from rice plants , 1 month culture on Botrytis cinerea (1MF), and 6 months culture on B. cinerea (6MF). 2) Nematode population was examined 10 , 20, 30 and 40 days after inoculation with 10 each of male and female adults per rice seedling. Each value is the mean of 10 replicates. 3) The figures with the same letter in the same column are not significantly different according to Duncan's multiple-range test (p=0.05).

Table 3. Body dimensions and body colour density index of female adults of Ditylenchus angustus from 40-day old culture depend- ing on host as a food.

1) Average of 50 female adults . 2) Based on a scale of 0-5 , where 0 means the most "transparent" and 5 means the most"dense dark". 3) Six months culture on Botrytis cinerea . 4) The figures with the same letters in the same column are not signifi- cantly different according to Duncan's multiple-range test (p=0.05).

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Fig. 4. Reproduction of Ditylenchus angustus on Botrytis cinerea in a test tube after inocula- tion with 10 each of male and female adults of the nematode obtained from rice

plant (•›) and from 6 months culture on B. cinerea (s). Vertical lines indicate standard errors.

A B

Fig. 5. Population structure of Ditylenchus angustus on Botrytis cinerea in a test tube after inoculation with 10 each of male and female adults of the nematode obtained from rice plants (A) and from 6 months culture on B. cinerea (B). Black column; 2nd stage juvenile, open column; 3rd stage juvenile, dotted column; 4th stage juvenile, stripped column; adults. rice plant rather than from 6MF. The maximum increase in the nematode population on B. cinerea on day 40 after inoculation from rice plant or 6MF was 291 or 229-fold larger than the inoculum population, respectively. The number of nematodes propagated from the two sources were significantly different from 20 days to onward (p=0.05) Fig. 5 shows the population structure of various developmental stages of the nematode on B. cinerea from rice plants and/or 6MF. Changes of the developmental components with time indicate that there was no increase in J4 or adults with ca. 50% of J2 and J3 until 20 days . On day 30, the components of J2 and J3 declined to 30% and on day 40 their population occupied 7-9

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of the total. On the other hand, the components of J4 and adults occupied 91-93%, in which adults were 52-55% and 34 38-39%.

DISCUSSION

Growth and reproductive parameters of the rice stem nematode D. angustus were investigat-

ed recently (1) on the fungal host, B. cinerea, on which the duration of one generation from egg

to egg was 10 days at 25•Ž. In the present investigation, the rice plant was employed as a host

to determine the life cycle and fecundity of D. angustus. On one-week-old rice seedling in a petri

dish the nematode completed one generation (from egg to egg) at 24-26•Žin 8 days. On B. cinerea

the total juvenile span of D. angustus was 6 days, i. e., 2 days each for 32, 33, and 34. On rice

plants 32 and 33 shortened their span to 1 day, and 34 took 2 days as on B. cinerea (Table 4). Accordingly, the total juvenile span took 4 days. The embryonic development was completed in

about 3 days (64-66 hr). The newly formed female adults started oviposition one day after

reaching adulthood. The total length of life cycle of D. angustus (from egg to egg) on (one-week-

old) rice seedlings (at 24-26•Ž) was about 8 days (190-200 hr). The life cycle of this nematode

resembles to on ground nut callus tissues; the duration of one generation

from adult to adult and the embryonic development until hatch were 8 and 2 days at 25•Ž,

respectively (22). At 16•Ž, these periods (for D. destructor) were prolonged to 12 and 4 days,

respectively. In case of D. dipsaci on onion seedlings the period of egg hatching and life cycle

from egg to egg at 15•Ž were 7 and 19-23 days, respectively (23).

Other life cycle parameters such as the intrinsic rate of natural increase on rice plant, cohort

generation time and net reproductive rate by which the number of offspring produced from a single female for a definite period can be predicted, were not determined due to difficulties

involved in recovery and reinoculation of a single female onto one-week-old rice seedlings.

Instead, the fecundity of the nematode on rice plants was investigated by inoculating a given

number of females with males and by recovering all the nematodes at intervals.

The results of fecundity experiment indicate that host as a food has a great effect on the fecundity of D. angustus. Between the two hosts, the original host rice plant was always superior to fungal host in supporting the growth and reproduction of the nematode. However, the reproduction of the nematodes on rice plant was greatly affected by the host on which they were

Table 4. Comparison of growth and propagation of Ditylenchus angustus continuously on rice plant and fungal mat of Botrytis cinerea.

1) This report . 2) ALT et al . (1995). 3) Nematode population size on 40 days after inoculation with 10 each of male and female adults.

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formerly cultivated. In this context, the rice plant also was superior to fungal host. The inocula

collected from fungal host resulted in lowered fecundity on rice plant as well on fungus. Whether

long or short period of nematode culture on fungus was also responsible to the reduction of

nematode fecundity on rice plant, like Aphelenchus avenae (14) and Bursaphlenchus xylophilus

(13) in which prolonged culture on the same fungal host resulted in lowered reproductivity and

decreased pathogenecity.

The differences in population size on between rice and fungal host were great. One of the

many factors determining the size of nematode population is the length of life cycle (19). The

shorter length of life cycle on rice plants was surely conducive to a greater size of population.

The second factor was the host growing condition, i. e., the capacity of the host to provide

nematodes with nutrients enough to increase the population. On fungal host, 30 days after

inoculation, the hyphae of B. cinerea were almost eaten up and virtually all fungal hyphae were

consumed on 40 days. Consequently, the nematodes at this stage became transparent, may be due

to low lipid contents in their body, and multiplication almost ceased. On the other hand, the rice

plants were still in growing conditions with varying degrees of infection symptoms and the multiplication of nematodes was still maintained.

The developmental stage of nematodes at the end of host growth, was almost composed of

J4 and adults. On day 40 when the fungal hyphae almost disappeared, J4 and adults were 91-93%

of the total population. Contrarily, on rice plants on that time there was no accumulation of these

developmental stages, though these stages were comparatively higher components along with

maximum multiplication; 83% of 6567/g wet tissues from rice to rice plant and 70% of 4818/g

from 6MF to rice plant (Table 1).

The present experiments support BUTLER'S suggestion that the innermost leaf-fold of rice

plant prevents the nematodes from moving to the topmost growing point due to its compactness

(5). As a result, the seedlings with such a heavy nematode population can survive and continue

to grow. Thus the rice plant as a host ensures the constant supply of nutrients to the nematodes

and on 40 days there was no sign of putative lipid consumption in the nematode body (Table 3).

The condition for nematodes inside a petri dish naturally dose not exist in the field situations

of rice plants. Inside the petri dish the relative humidity is kept by 100%. The favorable factors

for infection, disease development and reproduction of D. angustus are supposedly 28-30•Ž and

80% or more relative humidity (16). Under the natural conditions, the number of nematodes in

a stem of rice plants varies from 1000 to 3000 (7), but it occasionally reaches up to 30,000/stem

(6). Though the temperature inside the petri dishes was 24-26•Ž, the high relative humidity

should have provided nematodes with favorable conditions for infection and reproduction. Over

a period of 3 to 4 months in pottery pots in a glass house, D. angustus multiplied to 2505 and 3096/g wet tissues (12) from the initial population of 250-300, whereas in the present experiments , over a period of 30 to 40 days from the initial population with only 20, the nematodes multiplied to 4605

and 6576/g wet tissues of rice, respectively. Under field conditions, most nematodes are generally

located in the stems, especially in the upper half and the panicles, feeding on young growing tissues (3). The nematodes inside petri dish can be seen on whole plant surface, i. e., on both sides

of the leaf blades and also on the surface of the outermost leaf sheath of stems.

Ditylenchus angustus migrates from diseased plants to healthy plants on water and through stem and leaf contact under high humidity (21). Ufra disease is most severe in years with heavy

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precipitation and in highly humid regions in Bangladesh where the average rainfall exceeds 1.6m (8) and also in Vietnam, the disease is most severe in months of heavy rainfall or in fields with high water levels (9). The findings in the present experiments, i. e., shorter generation time of the nematode with the capability of rapid multiplication on the whole surface of the host plant under high humid condition and with the trait of leaving the host when the population reaches the maximum may be possible reasons for the above epidemic dissemination of ufra disease under specific conditions. The results of the present experiments on life cycle of D. angustus on rice plant and fecundity on both rice plant and fungal host together with weather information may contribute to the efficient management of ufra problem in tropical areas.

ACKNOWLEDGMENT

We thank the criticism from Dr. E. KONDO of Saga University.

REFERENCES

1) ALI, M. R, ISHIBASHI,N. & KONDO,E. (1995) Growth and reproductive parameters of the rice stem nematode Ditylenchus angustus on Botrytis cinerea. Jpn. J. Nematol. 25, 17-24. 2) BAKR,M. A. (1977) Occurrence of ufra disease in transplanted rice. Int. Rice Res. Newslt. 3, 16. 3) BRIDGE,J., Luc, M. & PLOWRIGHT,R. A. (1990) Nematode parasites of rice. In: Plant Parasitic Nematodes in Subtropical and Tropical Agriculture, (Luc, M., SIKORA,R. A. & BRIDGE.J., eds.) CAB Int. Inst. Parasitol., UK. 69-108. 4) BUTLER,E. J. (1913) An eel worm disease of rice. Bull. Agric. Res. Inst. Pusa, India. 34, 37pp. 5) BUTLER,E. J. (1919) The rice worm (Tylenchus angustus) and its control. Memoirs of the Department of agriculture in India, Botanical series, 10, 1-37. 6) CATLING,H. D., Cox, P. G., IsLAM,Z. & RAHMAN,L. (1979) Two destructive pests of deep water rice, yellow stem borer and ufra. ADAB News. 6, 16-21. 7) Cox, P. G. & RAHMAN,M. L. (1979) The ufra nematode population in deep water rice in Bangladesh. Int. Rice Res. Newslt. 4, 10-11. 8) Cox, P. G. & RAHMAN,M. L. (1980) Effects of ufra disease on yield loss of deep water rice in Bangladesh. Tropical Pest Management, 26, 410-415. 9) Cuc, N. T. T. & KINH, D. N. (1981) Rice stem nematode disease in Vietnam. Int. Rice Res. Newsl. 6, 14-15. 10) GAMBORG,O. L., MILLER,R. A. & OJIMA.K. (1968) Nutrient requirement of suspension cultures of soybean root cells. Exp. Cell Res. 50, 151-158. 11) IBRAHIM,S. K. & PERRY,R. N. (1992) Desiccation survival of the rice stem nematode, Ditylenchus angustus. Fundam. appl. Nematol. 16, 31-38. 12) IBRAHIM,S. K. & PERRY, R. N. (1994) Infectivity and population dynamics of the rice stem nematode, Ditylenchus angustus. Nematologica. 40, 412-422. 13) ISHIBASHI,N. & KONDO,E. (1977) Occurrence and survival of the dispersal forms of pine wood nematode, Bursaphelenchus lignicolus (MAMIYAand KIYOHARA).Appl. Entomol. Zool. 12, 293-302. 14) MANKAU,R. & MANKAU,S. K. (1963) The role of mycophagous nematode in the soil. 1. The relationship of Aphelenchus avenae to phytopathogenic fungi. Proceedings of the colloquium on soil fauna, soil microflora and their relationship. September, 1962, The Netherlands, 271-280. 15) MIAH, S. A. (1984) Disease problems and progress of research on ufra disease of rice in Bangladesh. Int. Rice Res. Newsl. 2, 35-38. 16) MIAH, S. A. & BAKR.M. A. (1977) Nematode disease of root. In: Lit. Rev. of Insect pests and disease of rice. BRRI, 125-129.

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17) MIAH, S. A. & RAHMAN,L. (1981) Observation on incidence and chemical control of ufra in Boro fields. Int. Rice Res. Newslt. 6, 12. 18) MONDAL,A. H., RAHMAN,M. L. & MIAH,S. A. (1989) Yield loss due to transplanting of ufra infected seedlings of rice. Bangladesh J. Botany. 18, 67-72. 19) NORTON,D. C. (1978) Ecology of Plant Parasitic Nematodes. John Wiley & Sons, New York, 268 pp. 20) PLOWRIGHT,R. A. & AKEHURST,T. E. (1992) Monoxenic culture of the ufra nematode Ditylenchus angustus. Fundam. appl. Nematol. 15, 327-330. 21) RAHMAN,M. L. & EVANS, A. A. F. (1988) Studies on host-parasite relationship of rice stem nematode, Ditylenchus angustus (Nematoda: ) on rice, Oryza sativa. Nematologica 33, 451-459. 22) WAELE,D. D. & WILKEN,R. (1990) Effect of temperature on the in vitro reproduction of Ditylenchus destructor isolated from groundnut. Revue Nematol. 13, 171-174. 23) YUKSEL,H. S. (1960) Some observations on the life cycle of on onion seedlings. Nematologica 5, 289-296. Accepted for publication: January 23, 1996.

和文摘要

イネ クキセ ンチ ュ ウの発 育 と繁 殖:灰 色 か び病 菌摂 食 と イ ネ稚 苗 寄生 の 比較

Md.Rustom ALI・ 石 橋 信 義

イネ クキセンチ ュウDitylenchus angustusの 卵期か ら卵期 まで の1世 代 は、 イネ稚 苗(ペ トリ皿内 B-5寒 天培地上 で発芽後1週 齢 のイ ネ稚苗)に 接種 した場 合、24-26℃ で8日 であ った(灰 色 かび 病菌 を餌 として生育 させた もの よ り2日 はやい。既報)。 卵 は2細 胞 期で産下 され、産卵 後64-66時 間 で2期 幼 虫が孵化 した。産卵後 の2期 、3期 幼 虫期間 はそれぞれ1日 、4期 幼虫期 間 は2日 で あった。 雌成虫 は成 虫 となって1日 経過 した後 、産卵 を開始 した(本 線虫 は両性 生殖)。 イ ネ体 に寄生 させ た場 合、本線虫 の産卵 能力 は灰色 かび病菌Botrytis cinereaを 餌 とす るよ りも常 に遥 か に大 きか った。本線 虫 を1ヶ 月(1MF)ま た は6ヶ 月(6MF)灰 色 か び病菌 で繁殖 させ た後 、イ ネ稚苗 に接種 す ると、 イネ体 での繁殖 は低下 した。即 ち、接種 頭数20頭(雌 雄10頭 ずつ)か ら出発 して40日 後 、1MFの 線 虫 は734倍 、6MFの 線虫 は993倍 、 イネ体で維持 して きた線虫 は1067倍 に増加 した。6MFと イネ体 で維持 して きた線虫 を、上 と同様 な条件 で灰色 かび病 菌 に接種 した場合 は、 それ ぞれ229倍 、291倍 に 増 殖 した。

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