Isolates Of Ectomycorrhizal Fungi Research Articles

Studies on the systematics of ectomycorrhizal fungi in axenic culture. II. The enzymatic degradation of selected carbon and nitrogen compounds

Ninety-six species of ectomycorrhizal fungi from 30 genera were grown on modified Melin–Norkrans agar where the carbon (glucose) or nitrogen (ammonium phosphate dibasic) supply was replaced by cellulose, lignin, pectin, lipid, amylose, gelatin, casamino acids, or urea. Ectomycorrhizal fungi did not appreciably degrade cellulose, lignin, or pectin. The remaining compounds were broken down by representatives of certain taxonomic groups. Lipase was produced by Amanita species, amylase by species of Amanita and Cortinarius, gelatinase by Piloderma, Thelephora, species of Lactarius section Dapetes, and some species of both Amanita and Cortinarius. Casamino acids were degraded by Laccaria, Hebeloma, and some Tricholoma species. Urease was detected in species of Hebeloma and Laccaria. The ability to enzymatically degrade selected carbon and nitrogen compounds have potential as taxonomic characters for the identification of isolates of ectomycorrhizal fungi. The significance of these results are also discussed in relation to the ecology of these fungi. Key words: ectomycorrhizal fungi, enzyme activity, cultures, identification, systematics.

Absence of Conidia as a Morphological Character in Ectomycorrhizal Fungi

An examination of 169 isolates of ectomycorrhizal fungi representing 96 species from 30 different genera revealed the absence of conidial anamorphs in vitro. Such findings confirm previous investigations by other researchers but some reports of conidial anamorphs exist. These anomalies are reinterpreted and attributed either to contaminants, saprobic species misidentified as ectomycorrhizal, or non-conidial structures misinterpreted as conidia. Conidial anamorphs may have been selected against in ectomy? corrhizal fungi in favor of the basidiospore for dissemination and infection.

Pure culture response of ectomycorrhizal fungi to imposed water stress

The ability of ectomycorrhizal fungal isolates to tolerate imposed water stress in pure culture was examined in 55 isolates of 18 species. Water potential treatments, adjusted with polyethylene glycol, were applied to Petri dish units. These units allowed colony diameter measurements of fungi grown on liquid media. Delayed growth initiation and inhibition of growth rate occurred with increasing water stress. For 87% of the isolates, growth rate was inhibited by the initial water potential treatment applied, leaving only seven isolates where growth increased with initial water potential treatments. No growth was evident under the imposed stress treatments for isolates of Laccaria bicolor, Laccaria laccata, and Lactarius controversus; growth occurred only in the control. Drought tolerant species, demonstrated by an ability to grow at a water potential of −3 MPa, included Boletus edulis, Cenococcum geophilum, Rhizopogon vinicolor, and five out of eight Suillus species. Species intolerant of −1 MPa included Hebeloma crustuliniforme, Laccaria bicolor, Laccaria laccata, and Suillus caerulescens. Fungal drought tolerance was poorly correlated with estimates of annual precipitation for collection locations. Estimates of drought tolerance seems to depend more on fungal classification than on annual precipitation at the site of collection. Reisolation of Laccaria bicolor increased growth rate and water stress tolerance when compared with the same fungus prior to reisolation.

The effects of ozone and sulfur dioxide on respiration of ectomycorrhizal fungi

Oxygen-uptake determinations were made on mycelial mats of four ectomycorrhizal fungal isolates: three of Pisolithustinctorius (Pers.) Coker and Couch and one of Thelephoraterrestris (Erhr.) Fr. following a 1-h exposure to 5 and 50 parts per hundred million (pphm) O3 or SO2. Similar determinations were made on mycorrhizal (P. tinctorius and T. terrestris) and nonmyeorrhizal loblolly pine (Pinustaeda L.) root segments exposed to 5 pphm O3 and SO2. Both gases caused marked reductions in respiration rates of the pure fungal and root materials with significant species and intraspecies differences observed. However, greater inhibition was observed with SO2 than with O3. Ectomycorrhizal loblolly pine root segments were significantly more resistant to the deleterious influences of O3 and SO2 on respiration than were nonmycorrhizal roots indicating that ectomycorrhizal development may afford some protection against feeder-root damage from O3 and SO2. The greatest protection from O3 was provided by Thelephoraterrestris while Pisolithustinctorius root sections were most resistant to SO2 damage.