Biological Control of Typhula Ishikariensis on Perennial Ryegrass
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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 orchard- grass 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 antago- nists 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 snow- melt. 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