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The mycelial growth, sclerotial production, and carbon utilization of the snow mould biocontrol agent Typhula phacorrhiza Fries were compared with the two grey snow mould fungi, Typhula ishikariensis Imai and Typhula incarnata Lasch ex Fries. Variation was observed among the four isolates for each species, but there was greater variation among species. All three species were able to grow at the lowest temperature (0°C), but temperature optima differed with T. ishikariensis lowest and T. phacorrhiza highest. On potato dextrose agar or potato malt agar at 10°C, T. phacorrhiza had greater radial growth than T. ishikariensis but less than T. incarnata. All species could utilize microcrystalline cellulose, bacto-cellulose, and glucose as carbon sources, but radial growth of T. phacorrhiza was significantly greater than T. incarnata and T. ishikariensis on these defined carbon sources tested, except for Indulin-AT, which was inhibitory to T. incarnata and T. phacorrhiza. This greater ability to utilize these structural and storage carbohydrates, combined with mycelial growth and sclerotial production over a wider range of temperatures, may help explain how some isolates of T. phacorrhiza are able to outcompete grey snow mould in field tests.Key words: turfgrass disease, biocontrol, psychrophilic.

Isolates of the fungus Typhula phacorrhiza Fries (TP) were evaluated in field tests over a 3-year period for suppression of grey snow mould caused by Typhula ishikariensis Imai (Tish) and Typhula incarnata Lasch ex Fr. (Tinc). Isolates of TP were collected across southern Ontario in the spring of 1994. In December 1994, 46 of these isolates, which had been cultured on mixed grains, were applied to creeping bent grass (Agrostis stolonifera L.) at a rate of 200 g/m2 (4 × 105 colony forming units (cfu)/m2) with inoculum of Tish or Tinc at 10 g/m2 (2 × 104 cfu/m2). In December 1995, 30 selected TP isolates were inoculated onto a new set of plots along with grey snow mould fungi. In November 1996, 22 of these isolates were re-inoculated onto the 1995 plots. All plots were rated for injury after snowmelt, 1995-1997. Isolates of TP varied significantly in their ability to suppress disease. No strong correlations were found between in vitro growth characteristics and field performance; however, significant positive correlations were found between the disease suppression trials for the 3 years, with several isolates showing statistically significant control of grey snow mould equal to a fungicide treatment.Key words: biocontrol, turfgrass disease, fungi.

Vegetative compatibility groups of Typhula ishikariensis biotype A include different isolates from various localities, and the most prevalent one (super vegetative compatibility group) was studied to reveal that this super group consisted of several genets existing throughout the habitat of T. ishikariensis biotype A in Hokkaido, Japan. Random amplified polymorphic DNA and mating incompatibility alleles were studied for 10 isolates belonging to the super vegetative compatibility group from two localities 250 km distant from each other and for five isolates belonging to different groups. Seven primers, which distinguished vegetative compatibility groups, were screened out of 60 and produced a total of 55 bands. The 10 super group isolates were divided into 5 subgroups, and the five unique isolates did not cluster with each other. Protoplasts were produced from each isolate to obtain monokaryons. They were then mated with tester monokaryons derived from basidiospores of two parental isolates, one of which belonged to the super vegetative compatibility group. Mating patterns suggested that the 10 super group isolates shared common mating incompatibility alleles but this was not the case with those belonging to unique groups. The super vegetative compatibility group was found to consist of several genets with many ramets distributed throughout the habitat of T. ishikariensis biotype A in Hokkaido. These genets were regarded as sib-related dikaryons derived from basidiospores. Keywords: Typhula ishikariensis, snow mold, genet, RAPD, mating incompatibility.

Speckled snow mould (caused by Typhula ishikariensis) is a potential threat to winter wheat (Triticum aestivum L.) production in eastern Canada. Information on the inheritance of snow mould resistance is needed to develop an effective breeding strategy. In this study, the inheritance of resistance to the speckled snow mould was examined using crosses of a resistant genotype, PI 173438, and four susceptible cultivars, Lennox, Kitami-2, Norin-8 and Ena. The parental lines, and the F1 and F2 populations from each of the four crosses were grown in the field and in an unheated plastic greenhouse and scored for snow mould resistance. Biomass yield, survival, plant height and number of tillers/plant, all expressed as percentage of check plants, were used as indices of snow mould resistance. Generation means analysis, combining data from the field and greenhouse experiments, indicated that snow mould resistance was largely influenced by environmental conditions, and that additive genetic effects were more important than epistatic effects in controlling the expression of the disease. Dominance effects oriented towards susceptibility were detected in only one of the four crosses. Estimates of broad sense heritability in the four F2 populations ranged from 0.62 to 0.96 and from 0.34 to 0.79, respectively, when biomass yield and number of tillers/plant were used as indices of snow mould resistance. When plant height was used as an index of snow mould resistance, the heritability estimates ranged from 0.10 to 0.53. Key words: Wheat (winter), Triticum aestivum, speckled snow mould, Typhula ishikariensis, heritability

Population structure of Typhula incarnata and Typhula ishikariensis, snow mold fungi, was determined by vegetative incompatibility on agar plates using isolates from 10 sites that differed in the extent of disturbance. Typhula incarnata populations were always diverse, with many different vegetative compatibility groups regardless of habitat differences, whereas diversity of T. ishikariensis populations differed according to habitat. Typhula ishikariensis populations in uncultivated lands were diverse; however, those from agricultural fields planted with perennial grasses became simpler with increasing number of years after the establishment of the host plant community. As a population, isolates from a new habitat were fast growers, less aggressive, and less competitive, and their sclerotia tended to germinate more rapidly than those from an old habitat. Where host plants were annual and the habitat was disturbed annually by tillage, population structure of T. ishikariensis was very simple. These results are discussed in terms of epidemiological differences between the pathogens and the effect of cultivation on population structure change. Key words: Typhula incarnata, Typhula ishikariensis, population structure, disturbance, snow mold fungi.

Isolates of the snow mold fungus, Typhula ishikariensis, were collected from seven localities in northern Japan where snow cover conditions differ. The isolates were identified as T. ishikariensis biotype B, which produces large sclerotia, biotype C with smaller sclerotia, and large sclerotial and intermediate forms. Mating experiments with tester monokaryons indicated that all populations were related. Populations from localities with deep, persistent snow cover produced larger sclerotia, which germinated more readily carpogenically (biotype B and the large sclerotial form) than those from localities where snow cover was shorter and intermittent (biotype C). The aggressiveness of the former was more variable, whereas the latter was without exception aggressive. There was no apparent correlation between growth rate at 0 °C and duration of snow cover. It was concluded that biotype C has been selected for localities with ephemeral snow cover, but that biotypes B and C and the related forms do not form distinct populations and should be regarded as a single taxon.

On genetical evidence Typhula FW, T. idahoensis Remsberg, and T. ishikariensis lmai should be considered as one species, and by priority the T. ishikariensis applied to it. Based on morphological characters the following taxonomic ranking is suggested: T. ishikariensis Imai var. ishikariensis, T. ishikariensis Imai var. idahoensis (Remsberg) comb.nov., T.ishikariensis Imai var. canadensis Smith & Årsvoll var.nov.Within this Typhula complex the latter two varieties differ most clearly morphologically, but are most closely related genetically. They are both found only in North America, while var. ishikariensis also occurs in Europe and Asia. Var. canadensis can be distinguished morphologically from the other two varieties by its smaller sclerotia and sporophores, by its more profuse production of aerial mycelium in culture, and the tendency of its sclerotia to be produced in bands, radial rows, and suspended in the aerial mycelium rather than in concentric rings. The only reasonably reliable way of separating the other two varieties is on sclerotial characters. Rind cells of var. idahoensis are more irregular in outline, with more lobate, occasionally digitate cells than var. ishikariensis.

The life-history strategies of Typhula incarnata and T. ishikariensis, the snow mold fungi, were studied in culture experiments. Radial mycelial growth at 0 °C, a temperature at which they thrive under natural conditions, was about half that of growth at the near-optimal temperature, 10 °C. However, when the colonies were covered with unsterile soil, mycelial growth at 0 °C was much greater than at 10 °C. Sclerotium production by T. incarnata was rapid in the latter half of the culture period, and sclerotium maturation was promoted by selected fungi. Typhula incarnata produced sclerotia frequently along the junction with colonies of selected fungi. Typhula ishikariensis biotype A produced the highest percent sclerotial biomass. Sclerotium maturation, i.e., pigmentation, was not stimulated by the selected fungi, but sclerotium production was moderately frequent in dual cultures with them. Typhula ishikariensis biotypes B and C produced the lowest percent sclerotial biomass. Their sclerotium maturation was rapid but not stimulated by the selected fungi. These findings suggest that although these snow mold fungi are, as a whole, stress tolerant, T. incarnata is relatively ruderal, T. ishikariensis biotype A is typically stress tolerant, and T. ishikariensis biotypes B and C are adapted to habitats with high stress and high disturbance.

A previously undescribed, sclerotial, low-temperature-tolerant fungus with orange sclerotia, is common on a wide range of plant species and substrates in Western Canada. It is often associated with snow mold complexes. It has also been found in eastern Canada and Norway, indicating a circumpolar distribution. It is described as Acremonium boreale n.sp. Some isolates were antagonistic towards common snow molds, viz. Fusarium nivale, Sclerotica borealis, Typhula ishikariensis var. ishikariensis and var. canadensis, and the nonsclerotial low-temperature basidiomycete in culture at low temperatures. Although it was weakly parasitic towards two grass species, its main ecological importance seems to be as an invasive primary saprophyte on a wide range of substrates. It may play a significant role in determining the nature and intensity of damage in snow mold complexes.

We identified 16allelesof the A and 17of the B incompatibility factors within 18 dikaryons of T. ishikariensis, a tetrapolar basidiomycete. A 1:1 ratio of alleles of the A and B incompatibility factors was previously reported for T. idahoensis and for T. incarnata.

Survivorship patterns of sclerotia of Typhula incarnata Lasch:Fr. and of T. ishikariensis S. Imai biotype A were compared under field conditions from May to November, using plastic containers with 10- or 250-μm mesh. Minute arthropods always existed in the 250 μm mesh containers, but the difference in mesh size did not affect the viability of sclerotia. Percent viable sclerotia of T. incarnata decreased from 86.0 to 24.2 for those placed on the soil surface, to 5.0% for those buried in soil 81 days after treatment, and then remained the same until the end of the experiment. Most of the T. ishikariensis biotype A sclerotia survived; however, in some containers buried in the soil, half to all of the sclerotia were dead. Several mycoparasites were isolated from both types of sclerotia. The possibility of biological control by reducing the number of sclerotia is discussed in relation to the difference in epidemiology of Typhula incarnata and T. ishikariensis biotype A.