Biological Control of Typhula Ishikariensis on Perennial Ryegrass

日植病報 58: 741-751 (1992) Ann. Phytopath. Soc. Japan 58: 741-751 (1992)

Biological Control of Typhula ishikariensis on Perennial Ryegrass

Naoyuki MATSUMOTO* and Akitoshi TAJIMI**

Abstract Low-temperature fungi were collected from plants just after snowmelt, and their antagonistic activity against Typhula ishikariensis, a snow mold fungus, was determined using orchardgrass seedlings. Isolates from gramineous plant debris, considered to be T. phacorrhiza, suppressed the disease caused by T. ishikariensis biotype A or B. Antagonists differed in their effectiveness against these biotypes. Isolates antagonistic to biotype A, which is the principal snow mold of perennial ryegrass in northern Hokkaido, were localized in this district. Despite prolonged snow, susceptible, perennial ryegrass is success- fully grown there. These findings suggest the natural occurrence of biological control of the disease in perennial ryegrass pastures in northern Hokkaido. Ground tissues of orchardgrass or alfalfa reduced activities of antagonists when mixed in the inoculum. Plant litter such as fallen maple leaves and rice straw favored antagonism. Application of the antagonists in a naturally infested field planted with perennial ryegrass resulted in an yield increase of 26.5% compared with the untreated control where fall cutting favored the occurrence of snow mold. Where plants were not cut in fall and snow mold damage was slight, yield increase was insignificant. (Received April 3, 1992)

Key words: biological control, snow mold, perennial ryegrass, Typhula ishikariensis.

INTRODUCTION

Perennial ryegrass (Lolium perenne L.) is widely grown in temperate regions as it has excellent qualities such as high digestibility and palatability to cattle. However in the past this crop has seldom been cultivated in areas with high snow cover where snow mold prevails1). Herbage production by perennial ryegrass is vigorous in fall while that of orchardgrass (Dactylis glomerata L.) is high in spring but low in fall. Thus cultivation of both crops would stabilize seasonal fluctuation in herbage production. For this reason, planted areas of perennial ryegrass are increasing in northern Hokkaido where snow persists during winter months5,21,22), but careful management is required to overcome the threat of speckled snow mold caused by Typhula spp.17,20) Matsumoto8,9) considered the possibility of biological control of speckled snow mold caused by T. ishikariensis S. Imai due to its ecological characteristics. Thus poor diversity in active microflora under snow cover may facilitate the introduction and establishment of antagonists so long as they are low-temperature tolerant, and the pathogen is K-selected. Preliminary experiments with Italian ryegrass (Lolium multiflorum Lam.), which is less winter hardy and more susceptible to snow mold, revealed the effectiveness of Typhula sp. as an antagonist. As a result there was doubling of the yield of the first cutting in a field naturally infested with snow mold11). Burpee et al.2) succeeded in suppressing snow mold caused by T. ishikariensis var. ishikariensis on creeping bentgrass (Agrostis palustris Huds.) using

* Hokkaido National Agricultural Experiment Station , 1 Hitsujigaoka, Toyohira-ku, Sapporo 062, Japan 北海道農業試験場 ** Present address: National Grassland Research Institute , Senbonmatsu, Nishinasuno, Tochigi 329-27, Japan 現在:草地試験場 742 日本植物病理学会報第58巻第5号平成4年12月

an isolate of antagonistic T. phacorrhiza Fr.

We collected low-temperature tolerant fungi including Typhula spp. from snowy areas of northern

Japan to determine their ability to suppress speckled snow mold. Distibution patterns of antagonists suggested the natural occurrence of biological control in perennial ryegrass fields in northern Hokkaido.

The effectiveness of biological control by selected isolates of Typhula spp. was then investigated in a perennial ryegrass field naturally infested with T. ishikariensis biotype A.

MATERIALS AND METHODS

Screening for antagonists. Fungal materials were collected from northern Japan after snowmelt. Isolations were made on potato-dextrose agar (PDA) supplemented with lactic acid and streptomy- cin at 10•Ž after surface-sterilization in 70% ethanol for 5sec and in sodium hypochlorite solution

(0.125% active chlorine) for 5min. Fungal isolates were subcultured on FDA slants at 4•Ž and those showing vigorous growth at this temperature were regarded as low-temperature tolerant, while others were discarded. Low-temperature isolates were obtained from Fukui, Toyama, Akita, Iwate, and

Hokkaido.

Screening consisted of two series of experiements. Low-temperature fungi examined in the first were heterogeneous and of diverse origin. They were divided into 6 categories: 1) saprophytic species of Typhula from plant debris of dicotyledons; 2) T. incarnata Lasch ex Fr., a weak pathogen known to suppress T. ishikariensis biotype B10); 3) an unknown low temperature basidiomycete with sclerotia causing •gsupponuke•h, crown rot, of winter wheat16), isolated from bentgrass; 4) Acremonium boreale

Smith & Davidson described as a low-temperature-tolerant, snow mold antagonist18); 5) Trichosporiella sp. and Trichosporon sp., nonsclerotial, low temperature hyphomycetes isolated from sclerotia of T. ishikariensis; and 6) isolates Sap and TOG-1, antagonist isolates of Typhula demonstrated in the preliminary experiments11). The second screening experiment was exclusively for Typhula isolates from debris of gramineous plants.

The antagonistic activity of low-temperature tolerant isolates was determined by the regrowth of plants which had received an inoculum mixture containing a pathogen and an isolate to be tested

(referred to as challanger). Either or both of T. ishikariensis biotypes A (isolate PR75D) and B (KWhi-1) were used as pathogens. Fungal cultures were grown on wheat-bran vermiculite (1:1, v/v) medium at

10•Ž for a month. An inoculum mixture of a pathogen and a challenger (1:1) weighing 65g was sprinkled over each plastic flat (45•~39•~7cm) containing 30 orchardgrass seedings (3-month-old) which had been hardened outdoors during November. Inoculated plants were incubated under snow cover for

65 days and then transferred to an unheated glasshouse to stop disease development and to promote regrowth of plants. After 10 days disease severity was determined on a scale of 0 (no damage) to 6

(plants killed). Plants inoculated only with pathogens weighing 65g were used as controls. Antagonistic capability of challengers was expressed as percent disease suppression according to the following equation:

disease severity of plants inoculated with pathogen-challenger mixture/ (1- disease severity of plants inoculated with pathogen )•~100

Amendments with organic matter. Two types of organic amendments were used to promote the efficacy of the known antagonists: organic matter from living plants, consisting of aerial plant parts of orchadgrass and alfalfa; and from dead materials, which included fallen leaves of maple, rice stave, peat compost, and bark compost. Apart from the two latter amendments all others were dried and pulverlized before use. Fungal inoculum weighing 65g was mixed with 5 or 10g organic matter from living plants or with 30g of dead materials. Further methods were the same as above. There were two replications.

Field experiments. •gFriend•h perennial ryegrass was sown in the spring of 1988 in 4m-long rows with 60cm intervals in a field of Hokkaido National Agricultural Experiment Station, Sapporo. No Ann. Phytopath. Soc. Japan 58 (5). December, 1992 743 treatment was made in the winter of 1988-89. Typhula incarnata and T. ishikariensis were the major snow mold pathogens the following spring. Sclerotinia borealis Bub. & Vleug. occurred infrequently. In

December, 1989, one half of the experimental field (referred to as plot A) was treated with 13 challengers including both effective and ineffective isolates (effective challengers were defined as those which showed more than 50% of disease suppression of either pathogen in screening experiments). Each row received 130g of wheat-bran vermiculite culture prepared as described above. Rows with fungicide

(copper 8-hydroxy quinoline) treatment or with no treatment were used as controls. There were 4 replications. The other half (plot B) was left untreated until the following year. Plot B was divided into two subplots, according to whether they were mowed or not mowed on October 1, 1990. In December, plot B was treated with five effective challengers. There were two replications. Plot A was not treated with a challenger nor fertilizers after the winter of 1990. The yield of first cutting was determined as fresh weight in mid-June each year.

RESULTS

Results from the first series of screening excluding Typhula sp. from debris of monocots (gramineous plants) are summarized in Table 1. Typhula spp. from dicots, the unknown •gsupponuke•h basidiomycete,

Acremonium boreale, Trichosporiella sp., or Trichosporon sp. were not antagonistic to either biotype of

Table 1. Disease suppression on orchardgrass seedlings by challengers of diverse origin excluding Typhula

sp. from gramineous plant debris a)

a) Values indicate percent disease suppression calculated as follows: disease severity of plants inoculated with pathogen-challenger mixture/

(1- disease severity of plants inoculated with pathogen )×100. b) Disease severity of control plants inoculated with T. ishikariensis biotype A or B was 5.3 and 5.85, respectively. c) not determined. 744 日本植物病理学会報第58巻第5号平成4年12月

Table 2. Virulence to orchardgrass seedlings and antagonism against Typhula ishikariensis biotype B in T. incarnata isolates a)

a) Values indicate disease severity (0=no damage, 6=killed). b) Disease severity of control plants inoculated with T. ishikariensis biotype B was 5.85. *** indicates significance at p=0 .001.

Fig. 1. Antagonistic capability of isolates of Typhula sp. from gramineous plant debris as determined by disease suppression on orchardgrass seedlings and their distribution in northern Japan. Each column represents each isolate. Black and white portions indicate antagonism against T. ishikariensis biotypes A and B, respectively. Black portions below horizontal axes and white portions above the axes show that the values are negative. Typhula ishikariensis biotype A predominates in the shaded region.

T. ishikariensis on orchardgrass seedlings. Isolates of T incarnate were, however, all antagonistic to T. ishikariensis biotype B with a mean percent disease suppression of 52.3, ranging from 31 to 75, and isolate variability was significant (Table 2). They were also pathogenic to orchardgrass seedlings with no isolate variability (Table 2). Their effectiveness as an antagonist, based on comparison in disease severity between plants inoculated with T. incarnata singly and those inoculated with both T. incarnate and T. ishikariensis biotype B, was evident in 4 isolates, i.e. YIR, 52-2, BY-3, and KSOG-3. There was no correlation between antagonism and virulence within T. incarnata isolates. Isolates of Typhula sp. from gramineous plant debris were antagonistic to varying degrees (Figs. 1 and 2). In general, isolates from Honshu were antagonistic to T. ishikariensis biotype B, but with little or no antagonism to biotype A. Isolates from Hokkaido, especially from Hamatonbetsu, northern Hokkaido were strongly antagonistic to biotype A and some of them were also antagonistic to biotype B. Amendments with organic matter from living plants reduced the effectiveness of the antagonists (Table 3). With no amendment biotype B was more vulnerable to antagonism from both isolates than biotype A. Both antagonists, i.e. Sap and TOG-1, were not pathogenic to orchardgrass seedlings with or Ann. Phytopath. Soc. Japan 58 (5). December, 1992 745

Fig. 2. Disease suppression of Typhula ishikariensis biotype A (right) or B (left) on orchardgrass seedlings by isolates of Typhula sp. from gramineous plant debris. Flats treated with the same antagonist isolates are arranged in pairs. Control flats treated with either pathogen are in the background.

Table 3. Effect of organic amendment with orchardgrass or alfalfa on antagonism when mixed in inoculum a)

a) Values indicates disease severity of 0 (no damage) to 6 (plants killed). Values followed by the same letter are not significantlydifferent according to Duncan's multiple range test (p=0.05). b) Sap, TOG-1:known antagonists; A: Typhula ishikariensisbiotype A; and B: biotype B. without amendment. Typhula ishikariensis biotype A was not affected by the antagonist Sap, while TOG-1 suppressed the disease caused by biotype A, but organic amendments nullified antagonism. Biotype B was vulnerable to antagonism from both isolates; however, with amendments, Sap became ineffective, and TOG-1 was nulified with orchardgrass amendment and became less effective with alfalfa amendment. Dead materials, on the contrary, promoted the antagonism by TOG-1 or did not change the level of antagonism (Table 4). Fallen maple leaves and rice straw significantly enhanced the effectiveness of TOG-1 while peat compost and bark compost were ineffective. The winter of 1989-90 was unusually warm with low snow fall. Consequently, there was little snow mold in plot A, as indicated by the small, insignificant difference between untreated control and fungicide treatment (Table 5). All the treatments including effective and ineffective challengers and fungicide application did not enhance the yield of the first cutting in plot A. The overall mean was 10.63 kg/row. Rows treated with effective challengers or fungicide showed significantly smaller (p=0.001) variation within replicates (mean CV=11.0%) than those treated with ineffective challengers or untreated control rows (18.2%). Challengers became established and they produced sclerotia the following 746 日本植物病理学会報第58巻第5号平成4年12月

Table 4. Effect of organic amendment with dead materials on antagonism when mixed in inoculum

a) TOG-1: known antagonist; B: Typhula ishikariensis biotype B. b) Values indicate disease severity (0=no damage, 6= killed). Values followed by the same letter are not significantly different according to Duncan's multiple range test (p=0.05).

Table 5. Effect of challengers from gramineous plant debris on the yield of first cutting of perennial ryegrass in a naturally infested field which survived two winters in plot A

a) Effective challengers whoes percent disease suppression was more than 50% against either pathogen in Table 3. b) Known antagonists.

Table 6. Yields of first cutting of perennial ryegrass rows treated in the fall two years previously in plot A a)

a) No treatments were made in the previous fall except mowing in a half of the plot.

spring and again in the third spring without their introduction the previous fall. The yield decreased drastically in the third spring even though no fertilizers were applied the previous year in plot A (Table 6): fall-mowed subplot produced herbage of 2.13, 2.60, and 1.78kg/row for effective-challenger-treated, i.e. Iwate 3, Sap, and KTF, fungicide-treated, and untreated control rows. There were no significant differences among treatments. In non-fall-mowed subplot, overall mean yield (3.22kg/row) was significantly higher (p=0.001) than fall-mowed subplot (2.15kg/row). The differences among treatments Ann. Phytopath. Soc. Japan 58 (5). December, 1992 747

Fig. 3. Comparison in the yield of first cutting of perennial ryegrass between rows treated with effective challengers, untreated control rows, and fugicide-treated rows in plot B.

were not significant in non-fall-mowed subplot, either; the yields for effective-challenger-treated, fungicide-treated, and untreated control rows, were 2.98, 3.95, and 3.18kg/row, respectively. The winter of 1990-91 was normal. Typhula ishikariensis biotype A occurred badly on perennial ryegrass in untreated control rows in plot B with plants showing extensive damage a month before snowmelt and no green leaves remaining on them (Plate I-A). In rows treated with effective challengers, the pathogen produced few sclerotia; green leaves survived sparsely (Plate I-B). Where challengers were introduced, they were found established with numerous sclerotia on plants (Plate I-C). In the fall-mowed subplot in plot B, effective challengers invariably and significantly (p=0.001) increased the yield of first cutting, but their effect was less in comparison with untreated control rows in the non-mowed subplot. Figure 3 indicates the comparison between treatments with a relative yield of non-mowed, untreated control rows of 100 (3.675kg/row). Since there was no isolate variability in yield increase, values for biocontrol rows were presented as a mean of five antagonists. In rows without fall mowing, the fungicide increased the yield, i.e. relative yield was 146, but the effective challengers were not effective in yield increase (relative yield 108). In the fall-mowed subplot, effective challengers increased the yield by 26.5%. Fall mowing greatly affected the yield of the first cutting; yield reduction as a result of fall mowing was only 4.5% in fungicide-treated rows, while untreated control rows showed a decrease in yield by as much as 36.3%. The effective challengers diminished the deleterious effect of fall mowing to 16.4% on average.

DISCUSSION

Biological control was successful in the third winter in a naturally infested field: in fall-mowed plot B, the introduction of effective challengers resulted in a significant yield increase of 26.5% as compared to untreated control; their effect was, however, insignificant in the second winter (plot A). This contrasts with Italian ryegrass used in the preliminary experiments11) as antagonists were found effective even in the first winter. Due to snow mold in Sapporo, plant survival of perennial ryegrass was reported to decrease significantly after the third wintery. Tezuka and Komeichi20) reported similar findings in Hamatonbetsu, northern Hokkaido. Perennial ryegrass plants deteriorate physiologicaly three years after seeding19) and consequently become vulnerable to the attack of snow mold. The date of final cutting has been the concern of grassland agronomists since forage crops were found to pass through a critical period before wintering and that they should not be cut at this time. In northern Hokkaido19), perennial ryegrass passes through a similar period in late October. When herbage is removed during this period, physiologic factors are considered to reduce plant survival greatly in the 748 日本植物病理学会報第58巻第5号平成4年12月 following spring13,14); however, in the present study, fall mowing did not directly result in poor regrowth in the following spring but significantly affected the occurrence of snow mold as was revealed by fungicide treatment. Cultural practices should thus affect the effectiveness of antagonists through the physiologic conditions of plants and possibly through saprophytic growth of both antagonists and pathogens. Late fall mowing to remove excessive vegetative growth of winter wheat predisposed plants to severe snow mold, while non-mowed plants recovered to some extent though their foliage was severely molded3). Further field experiments are required to determine a compromise how best to relate this critical period with biological control. Saprophytic growth of pathogens on deteriorating clipping was found to provide an inoculum source which accounted for increased snow mold3). Organic amendments with chitin and residues of wheat and barley after seeding increased the severity of snow mold on winter wheat possibly by enhancing the saprophytic growth prior to parasitic activity4). In the present study, the effect of organic amendments varied: ground alfalfa and orchardgrass reduced antagonism, but antagonism was enhanced by dead materials such as fallen maple leaves and rice straw. Availability of organic residues should be determined if they are utilized exclusively by antagonists. The effective challenger was considered to be isolates of T phacorrhiza judged by relatively large size and heavily interlocking rind cells of their sclerotia and occasional presence of a basal stalk15). Possibly they too are weak pathogens since they all originated from dead leaves which had been senescent but not dead before winter. Isolates of T. phacorrhiza in Canada show considerable variation: Burpee et al.2) reported that the isolates they used as a biocontrol agent were not pathogenic, while Schneider and Seaman15) found this fungus was pathogenic on winter wheat. Though the mechanism of antagonism has not been elucidated, Burpee et al.2) considered that competition for nutrition between T. ishikariensis var. ishikariensis and T. phacorrhiza was important in the suppression of gray snow mold by the former fungus on turfgrass. The niches of these two fungi are doubtlessly close. In this context, T. incarnate is competent as an antagonist provided its virulence is attenuated. We have not examined the range of virulence in T. incarnata, but there should be avirulent isolates. Some field isolates of T. ishikariensis biotype B were totally avirulent (Matsumoto, unpublished). Alternatively variation could be obtained by breeding since T. incarnate is highly sexual. Kiyomoto and Bruehl6) observed segregation of virulence within S1 progenies of a moderately virulent isolate of T. idahoensis Remsberg to find that 19% of the progenies were avurilent. Introduction and establishment of the antagonist were readily achieved presumably because vacant niches are relatively abundant under snow cover. Growth at low temperatures under snow cover is a major prerequisite for antagonists of snow mold. Production of numerous sclerotia in the field by the effective challengers is a measure of the success of their introduction and establishment. Lawton and Burpee7) considered that the residual activity of T. phacorrhiza was effective on turf, and this may also be true for grasslands. We found the production of numerious sclerotia by the challengers two years after introduction. In the 1960s from field trials in Sapporo, Murakami et al.12) concluded that ryegrasses including perennial ryegrass were unable to survive for many winters in Hokkaido and that, at most, practical cultivation was possible for 3-4 years. However, in northern Hokkaido, perennial ryegrass was found to grow for longer periods when more intensive cultural practices were used5,21,22).Antagonists from northern Hokkaido were notably more active especially on T. ishikariensis biotype A, which is the primary snow mold fungus on perennial ryegrass in that region. Antagonists from other localities were generally efective against biotype B, only. Localized distribution of antagonists of biotype A in northern Hokkaido suggests that successful cultivation of perennial ryegrass in this region despite of more prolonged snow cover is largely attributed to natural occurrence of biological control. Grasslands planted with perennial ryegrass are now also increasing in mountainous regions of Iwate and Aomori, northern Tohoku. There, T. ishikariensis biotype B is the main snow mold fungus and sclerotia of T phacorrhiza-like fungus are abundant (Matsumoto, unpublished). The estimate of T. phacorrhiza-like fungus as an antagonist may predict the future of perennial ryegrass pastures in these regions. Ann. Phytopath. Soc. Japan 58 (5). December, 1992 749

Thanks are due to the following colleagues for helping us collect fungal materials: T. Nakajima, K. Nakamura, K. Sato, Y. Sato, S. Takamatsu, S. Tsutsui, and H. Yaegashi. We are indebted to H.J. Willetts,

University of New South Wales, Australia for his critical reading of the manuscript.

Literature cited

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ryegrass, Lolium perenne L. Res. Bull. Hokkaido Natl. Agric. Exp. Stn. 114: 173-193 (in Japanese).

2. Burpee, L.L., Kaye, L.M., Goulty, L.G. and Lawton, M.B. (1987). Suppression of gray snow mold on

creeping bentgrass by an isolate of Typhula phacorrhiza. Plant Disease 71: 97-100. 3. Huber, D.M. and Hankins, B.J. (1974). Effect of fall mowing on snowmold of winter wheat. Plant Dis.

Reptr. 58: 432-434. 4. Huber, D.M. and Anderson, G.R. (1976). Effect of organic residues on snowmold of winter wheat.

Phytopathology 66: 1028-1032.

5. Ishida, S., Sumiyoshi, M., Nakamura, K., Kawasaki, T. and Ogura, N. (1989). Management of perennial ryegrass pasture mixed with orchardgrass and ladino clover in Tenpoku district. J. Hokkaido Grassl. Sci.

23: 22-26 (in Japanese).

6. Kiyomoto, R.K. and Bruehl, G.W. (1976). Sexual incompatibility and virulence in Typhula idahoensis. Phytopathology 66: 1001-1006.

7. Lawton, M.B. and Burpee, L.L. (1990). Effect of rate and frequency of application of Typhula phacorrhiza

on biological control of Typhula blight of creeping bentgrass. Phytopathology 80: 70-73. 8. Matsumoto, N. (1985). Perspective on biological control of snow mold. Hokuno 52 (11): 1-11 (in Japanese).

9. Matsumoto, N. (1988). Biological control of spekled snow mold. Shokubutuboueki 42: 231-234 (in

Japanese). 10. Matsumoto, N. and Sato, T. (1983). Niche separation in the pathogenic species of Typhula. Ann. Phytopath. Soc. Japan 49: 293-298.

11. Matsumoto, N. and Tajimi, A. (1985). Preliminary experiments for biological control of snow mold caused

by Typhula incarnata and T. ishikariensis. Proc. XVth International Grassland Congress, pp. 787-788. 12. Murakami, K., Kaneko, K., Kojima, S. and Sekijo, T. (1965). Varietal trials on ryegrass (Lolium sp.). Res.

Bull. Hokkaido Natl. Agric. Exp. Stn. 85: 68-76 (in Japanese).

13. Noshiro, M. and Hirashima, T. (1974). Pasture management in a cold region. IV. Influences of cutting and fertilization in autumn on the accumulation of reserve carbohydrates in grasses. Bull. Hokkaido Prefect.

Agric. Exp. Stn. 30: 75-84 (in Japanese). 14. Sakamoto, N. and Okumura, J. (1973). Growth characteristics and management of pasture crops from late

autumn to early spring. 1. Effects of cutting period of pasture in late autumn on yields in next spring. Bull.

Hokkaido Prefect. Agric. Exp. Stn. 28: 22-32 (in Japanese). 15. Schneider, E.F. and Seaman, W.L. (1986). Typhula phacorrhiza on winter wheat. Can. J. Plant Pathol. 8:

269-276. 16. Shimizu, M. and Miyajima, K. (1990). •gSupponuke•h syndrome on winter wheat. Ann. Phytopath. Soc.

Japan 56: 141-142 (Abstr. in Japanese). 17. Shimokoji, H., Yoshizawa, A. and Ozuchi, K. (1984). Effect of cutting date and nitrogen application in fall on winter survival of perennial ryegrass. J. Hokkaido Grassl. Sci. 18: 68-71 (in Japanese).

18. Smith, J.D. and Davidson, J.G.N. (1979). Acremonium boreale n. sp., a sclerotial, low-temperature-tolerant,

snow mold antagonist. Can. J. Bot. 57: 2122-2139. 19. Tezuka, M. (1977). Studies on adaptability of perennial ryegrass cultivars to the Tenpoku district. III.

Relationships between final cutting date and subsequent winter injury. J. Hokkaido Grassl. Sci. 11: 38-41

(in Japanese). 20. Tezuka, M. and Komeichi, M. (1980). Varietal differences in winter survival and productivity in late

autumn of perennial ryegrass in Tenpoku district. Bull. Hokkaido Pref. Agric. Exp. Stn. 44: 52-61 (in

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Sci. 22: 225-228 (in Japanese).

22. Yuto, K. (1986). A survey on perennial ryegrass cultivation in the Soya district. J. Hokkaido Grassl. Sci. 20: 118-121 (in Japanese). 750 日本植物病理学会報第58巻第5号平成4年12月

Plate I Ann. Phytopath. Soc. Japan 58 (5). December, 1992 751

和文摘要

松本直幸・但見明俊:ペレニアルライグラス雪腐黒色小粒菌核病の生物防除

融雪直後の植物より低温性の糸状菌を採集し,それらの雪腐黒色小粒菌核病菌(Typhula ishikariensis)に対する拮抗性を,オーチャードグラス幼苗を用いて評価した。イネ科植物残渣由来のT. phacorrhizaと考えられる菌株が,本病の拮抗菌として有効で,これらの菌株の拮抗性には変異がみられた。すなわち,本病菌生物型Bに拮抗性を示す菌株は積雪地帯に普遍的に分布していたが,ペレニアルライグラスの主要な雪腐病菌である生物型Aに有効な菌株は,北海道北部天北地方に局在していた。このことは,天北地方では生物防除が自然におこり,多雪にもかかわらず,本地方で雪腐病に弱いペレニアルライグラスが多く作付けされている理由の一つと考えられた。カエデの枯葉やイナワラは拮抗作用を促進し,アルファルファやオーチャードグラスの乾燥粉末は拮抗作用を低下させた。これらの拮抗菌を用いて,生物型Aの自然発生するペレニアルライグラス圃場で生物防除試験を行ったところ,発病のひどい条件下(3冬目, 秋期刈取処理をした区)では26.5%の増収をみた。また,根雪前に導入した拮抗菌は,翌春には植物体上に菌核を多数形成しており,本拮抗菌においては導入・定着が容易であることがわかった。

Explanation of plate

Plate I Field experiments on biological control of Typhula ishikariensis biotype A on perennial ryegrass. A. Damaged plants in an untreated row. B. Plants in a row treated with an antagonist isolate. C. Sclerotia produced on plants by an introduced antagonist.