Spore germination inHebeloma stimulated by living plant roots

Abstract

Basidiospores from 14 strains of Hebeloma (Agaricales) representing 5 groups of mycorrhiza-forming species were tested for germination on a nutrient agar medium. Germination occurred in 13 strains but never exceeded 0.1%. A 10fold increase or more in germination percentage was obtained in 4 out of 7 tested spore collections only by placing the growing root of a pine seedling among the spores on the agar medium.Basidiospores of mycorrhiza-forming Homobasidiomycetes generally do not germinate on ordinary agar media but require special conditions for germinationL However, in the genus Hebeloma (Cortinariaceae, Agaricales) where most species form ectomycorrhiza with trees, spore germination occurs readily within the section Denudata, subsection C, as was demonstrated by Bruchet 5. In other sections of Hebeloma he observed no, or merely a very sparse and slow, germination. It was thought that increased knowledge of the conditions for spore germination in Hebeloma might also contribute to the understanding of the spore germination mechanism in other, chiefly micorrhiza-forming genera, e.g. Inocybe and Cortinarius, of the family Cortinariaceae, in which spore germination in vitro has not yet been achieved. In some other Homobasidiomycetes the germination rate could be increased by using Rhodotorula yeast as an activator organism and/or by adding activated charcoal 4. Therefore these measures and some others were tested for their efficiency in improving the germination of spores from a number of Hebeloma species. 14 spore collections from fruit-bodies of Hebeloma were obtained in the autumn of 1978 and preserved in petri dishes under sterile conditions in darkness at 4 ~ Most of them came from habitats in the neighbourhood of Uppsala, Sweden. After spore-casting, the fruit-bodies were dried and sent to Dr G. Bruchet, Lyon, for determination. All of them could be identified as to section, subsection and stirpes, but some could not be given a definite species name because of the inadequacy of the material. However, the collections comprised at least 5 different species representing as many subsections or stirpes. The spore germination tests were made on plates of a semisynthetic nutrient agar medium 4. About 0.1 ml of a suspension containing 500,000-1,000,000 spores per ml was spread over the agar surface by means of a glass rod. In some experimental series a colony of Rhodotorula glutinis (Fres.) Harrison was inoculated onto each plate, or activated charcoal was dusted over half of the agar surface. The plates were sealed with parafilm and incubated in darkness at 25 ~ Because of the generally very sparse and varying germination, which did not take place simultaneously, no efforts were made to estimate the percentage germination exactly.Spores of all tested collections, except No. 568, germinated at least in 1 experiment (cf. table). The first germinations could usually be observed only after 2 or 3 weeks. New ones then gradually appeared, even after an incubation time of up to 5 months. In all cases the percentage germi...

Availability of Ectomycorrhizal Fungi to Black Spruce above the Present Treeline in Eastern Labrador

“…In fact, spores of many ECMF species may remain dormant until germination is triggered by the presence of a suitable host plant, such as an establishing seedling [73], [76], [77]. This indirect influence of ectomycorrhizal shrubs on soils not vegetated by ectomycorrhizal hosts appears to occur at the scale of our sampling sites, but does not seem to extend further, such as into the glacial moraine.…”

GERMINATION OF BASIDIOSPORES OF MYCORRHIZAL FUNGI IN THE RHIZOSPHERE OF PINUS RADIAT A D. DON

“…Four weeks after inoculation 34 and 31 % basidiospores of S. luteus and S. granulatus had germinated, respectively, while 46 % R. luteolus spores germinated under the same conditions. DISCUSSION Fries & Birraux (1980) and Birraux & Fries (1981) showed that when pine roots were placed on plates of nutrient agar seeded with basidiospores of the ectomycorrhizal fungi Hebeloma spp. and Thelephora terrestris Ehrh.…”

“…Although the rhizosphere is considerably richer in energy sources than is soil, the much longer generation time of bacteria in the rhizosphere than on laboratory media (Bowen & Rovira, 1976) indicates that it is certainly not an optimal medium. Fries & Birraux (1980) observed that certain young myeelia from germinated spores in synthetic media died for unknown reasons. However, the percentage germination obtained in these studies guarantees a good level of infection even if some germ tubes die off before they grow into infective mycelium.…”

“…Theodorou & Bowen (1973) examined mycorrhizal production as a function of numbers of basidiospores inoculated into soil and concluded that considerably greater germination had occurred in the presence of roots than on laboratory media. Fries & Birraux (1980) placed pine seedlings on agar media seeded with basidiospores of Hebeloma species and increased spore germination to about 1 %. Germination occurred close to the root suggesting stimulation by root exudates.…”

Germination and infectivity of ectomycorrhizal fungal spores in relation to their ecological traits during primary succession

“…Although host roots and root exudates improve EMF spore germination (Bowen, 1994, and references therein), the extent of the host effect on spore germination varies considerably (Fries, 1987). For example, pine ( Pinus radiata ) seedlings enhanced spore germination by up to 34 and 69% in species of Suillus and Rhizopogon , respectively (Theodorou & Bowen, 1987), whereas germination was as low as 1% in Hebeloma species (Fries & Birraux, 1980). To date, the causes of such variation in EMF spore germination are poorly understood.…”