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The genus Mesophellia, type of the family Mesophelliaceae, has been restudied in light of extensive recent collections. Most past species identifications in the genus have been erroneous, because past workers did not comprehensively study holotypes or fresh material. In this paper, the genus is divided into two subgenera: Mesophellia and Loculatae. Subgenus Mesophellia comprises 12 species, of which 8 are newly described here: M. angustispora, M. brevispora, M. clelandii, M. oleifera, M. pallidospora, M. pawa, M. rava and M. trabalis. Subgenus Loculatae comprises two species, both of which are newly described here: M. labyrinthina and M. westresii.

This paper describes two new genera of gastroid (truffle-like) Basidiomycotina. Royoungia boletoides is described from Cooloola, Queensland, and is tentatively assigned to the Boletales on the basis of sporocarp and spore morphology. Mycoamaranthus auriorbis is described from a number of collections from northern Queensland and is not placed in any currently described family.* Part II, Aust. Syst. Bot., 1992, 5, 597–611.

Re-examination of species ascribed to the genus Labyrinthomyces plus our collections of related undescribed taxa revealed three distinct morphological groups which we segregate at the generic level. All have globose to ellipsoid spores ornamented with amorphous, hyaline warts or ridges. Labyrinthomyces is retained as a monotypic genus characterised by a brown-tomentose peridium and paraphyses half as long as the asci. Dingleya contains six species (two newly described here) with tessellate-cracked to verrucose peridia. Reddellomyces has four species (one newly described) with white to pale brown, smooth peridia. The last two genera are known only from Australasia.*Part I, Aust. Syst. Bot., 1990, 3, 653–70.

Descolea maculata sp. nov. is described, illustrated and compared with other species of the genus. A Gondwanaland/Nothofagus origin proposed for the genus is discussed in the light of the Western Australian record. Ectomycorrhizae initiated by D. maculata on roots of Eucalyptus diversicolor and E. marginata, under both aseptic and non-sterile conditions, provide confirmation of the ectomycorrhizal status of the genus Descolea. Cystidia associated with the fungal mantle are similar to those reported for other mycorrhizal fungi of eucalypts.

Root exudates from seedling eucalypts were collected aseptically, analysed for sugars, amino acids and organic acids and an examination made of their effect on zoospore chemotaxis, mycelium growth and chlamydospore germination of Phytophthora cinnamomi. Seedlings of root-rot susceptible Eucalyptus marginata produced greater concentrations of sugar and amino acid exudates than the root-rot resistant Eucalyptus calophylla at all sampling times. There was, however, little qualitative difference between the eucalypt root exudates. Both eucalypts attracted zoospores to roots in culture tubes. Infection of the roots followed encystment and germination of the zoospores. Germination of chlamydospores and mycelium growth of P.cinnamomi was significantly increased by the presence of root exudates and no differences were observed between exudates of the two species. Only amino acids and organic acids stimulated germination of chlamydospores. It was concluded that differences in root-rot susceptibility of eucalypts to P.cinnamomi are not attributable to differences in root exudate from eucalypt seedlings.

Mycorrhizal root development was more frequent in Eucalyptus calophylla than in Eucalyptus marginata in field and pot samples of soil conductive to Phytophthora cinnamomi. Morphologically different types of mycorrhizas were also observed in the two species, which suggested preferential stimulation of mycorrhizal fungi, and this was supported by cross-inoculation experiments with fungal symbionts isolated from mycorrhizal roots and from basidiomycete sporophores. Isolation of bacteria from mycorrhizal roots, and low power electron microscope study of these roots, indicated a significant mycorrhizosphere effect. Populations of bacteria varied quantitatively and qualitatively for different mycorrhizal roots. In suppressive soil few mycorrhizal roots were formed in either species. It is suggested that the different types of mycorrhizal roots and their associated bacterial microflora may contribute to differential susceptibility of the two species to infection by P. cinnamomi in conducive soil.

Application of calcium carbonate to an acid sand (pH 4.5 in 1/5 0 . 01 M calcium chloride), which increased the soil pH to 6.7, increased the fresh weight of tops of jarrah seedlings and decreased the fresh weight of roots. Calcium carbonate markedly increased the proportion of fine roots and almost suppressed infection of jarrah roots by P. cinnamomi.

An investigation was made of the microflora associated with unsuberized roots of Eucalyptus marginata and Eucalyptus calophylla raised in different soils. The studies were made for 'conducive' lateritic soil (in which E. marginata is susceptible to infection by Phytophthora cinnamomi but E. Calophylla is resistant); and in 'suppressive' loam soil in which both eucalypt species are unaffected by the pathogen. Lateritic soil in some cases contained natural infection of P. cinnamomi. Rhizospheres of both species contained larger microflora populations (expressed as numbers per g of root) than in the soils. In general, the population of rhizosphere microflora was greater for E. Marginata than E. calophylla seedlings in the uninfected lateritic soil. Qualitative differences were also recorded in populations of bacteria, actinomycetes and fungi, and in particular, fluorescent pseudomonads were more numerous in the rhizosphere of E. marginata seedlings. Eucalypt seedlings raised in loam soil harboured greater microbial populations than in lateritic soil. This could in part be attributed to the higher nutrient and organic matter status of the loam. E. marginata had a greater total rhizosphere population, but actinomycetes were more numerous in the rhizosphere of E. calophylla. Qualitative differences in populations of bacteria, actinomycetes and fungi were also noted. In naturally infected lateritic soil the microflora populations were invariably lower than for the other soils. When the counts of bacteria and actinomycetes were expressed as numbers per mm2 of root surface, E. calophylla had a significantly higher number of propagules per unit area than E. marginata. The loam soil was an exception; there E. marginata had three times as many bacteria per unit area of the root surface as E. calophylla. It is suggested that the microflora population differences recorded for the two eucalypts in lateritic soil may contribute to the differential susceptibility of species to infection by P. cinnamomi; and that the higher populations of microflora in the loam soil contribute to the suppression of P. Cinnamomi in that soil.

In soils under forest conditions and on seedlings grown under glasshouse conditions jarrah mycorrhizae exhibited strong habitat preferences. Litter on the forest floor was the main site for the formation of the white and brown ectomycorrhizae, and removal of the litter layer by prescribed burning reduced by 90% the numbers of these two ectomycorrhizae. Black ectornycorrhizae were dominant in the mineral horizons of soil and were unaffected by the type of surface litter. In glasshouse experiments litter from different plant species significantly influenced formation of ectomycorrhizae by jarrah seedlings. Litter from Acacia pulchella R. Br. was favourable for formation of ectomycorrhizae but ectornycorrhizae were absent from Banksia grandis Willd. litter. Black ectomycorrhizae, Hysterangium- initiated ectomycorrhizae and vesicular arbuscular mycorrhizae formed on jarrah seedlings in the soils used in glasshouse studies. Addition of nitrogen and phosphorus to these soils influenced the relative abundance of mycorrhizae. It is postulated that inoculum levels, nutrient status of litter and soil and the presence of compounds inhibitory to fungal growth are critical in determining the abundance of mycorrhizae. Factors affecting formation of mycorrhizae by jarrah and the ecological implications of these results are discussed.

Three major morphological types of ectomycorrhizae have been distinguished on roots of Eucalyptus marginara (jarrah). These were broadly classified as white, brown and black types. The variation in type of ectornycorrhizae and number of infected tips with season and depth in the soil were monitored at three forest sites. The sites had been burnt 1 , 6 and 45 years before sampling. Formation of ectomycorrhizae occurred in winter and spring. The black type was found predominantly in the soil whilst the white and brown types were associated with litter. The mean number of ectomycorrhizal root tips was highest in the 45 year unburnt and least in the 1 year unburnt site, suggesting that burning history influences their abundance.

Native forest at Durras in south-eastern New South Wales and Jarrahdale in south-western Western Australia was examined for the presence of Phytophthora cinnamomi by two sampling and isolation techniques. With the lupin seeding baiting technique, randomly selected samples of soil and fine roots collected from the New South Wales site yielded P. cinnamomi when baited, while similar baiting of comparable samples from Western Australia failed. Direct plating of samples of upper roots and root collars of recently dead Banksia grandis from Western Australian sites yielded P. cinnamomi, while this organism was not isolated from comparable samples of chlorotic Macrozamia communis collected at the New South Wales site. The results suggest that the form of occurrence of P. cinnamomi and its association with disease in Australia vary in different situations. Viewing each situation independently might ensure the adoption of control/prevention strategies appropriate to all.