Graduate Thesis Or Dissertation
 

Enzyme activity and phytohormone production of ectomycorrhizal fungi

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  • The several thousand fungi known to form ectomycorrhizae have co-evolved with their host plants and have developed impressive physiological and ecological diversity. Exploration of some relationships of enzyme activities and phytohormone production of selected ectomycorrhizal fungi to distribution and tree hosts is reported in this thesis. The data have particular relevance to selection of isolates for inoculation of planting stock in forest nurseries, so variation between isolates within species was assessed as well as differences between species. Enzymatic activity, selected isozyme patterns, and phytohormone production were assayed for the fungi cultured in liquid medium composed of minerals and dextrose. The mycelium was tested for acid and alkaline phosphatase and nitrate reductase activities and chromatographed for isozyme patterns. Culture filtrates were extracted and measured for extracellular cytokinins, IAA (indoleacetic acid) and, in two cases, gibberellins. Nine genera, 24 species and 46 isolates of mycorrhizal fungi were included in the experiments. The level of enzymatic activity and the amount of extracellular phytohormones produced differed between species and within species of fungi. The data demonstrated that some of the variation among isolates was related to host tree species and environment. Tricholoma ponderosuni S-198 collected from Pinus contorta in coastal sand dunes showed high acid phosphatase and lower alkaline phosphatase than S-199 which was collected from Pseudotsuga menziesii at 1111 m elevation in the Oregon Coast Range. The two cultures also differed in pH optima. There were no significant differences between the two isolates in production of extracellular cytokinins or IAA (indoleacetic acid), and gibberellins were low for both. Differences in enzyme activity and phytohormone production were prominent among the six isolates of Laccaria laccata. The patterns of acid phosphatase isozyme could be clearly divided into three host related groups. An isolate from a forest nursery differed strikingly tn several characteristics from the other isolates, all of which were from a natural forest. This suggests that nursery soil management practices may select for particular edaphic ecotypes of mycorrhizal fungi. Eight isolates of Pisolithus tinctorius showed generally low acid and alkaline phosphatase activities and also low nitrate reductase activity. These ectomycorrhizal fungi are characteristic of xeric sites with rocky soil that is low in organophosphorus. Variation between isolates of P. tinctorius in phytohormone production was greater than for other fungi. This may account in part for the varied seedling response to ectomycorrhizal formation with this fungus. Thirteen cultures spanning six species of the genus Rhizopogon showed patterns of phosphatase isozyme related to infrageneric groups of the species and also to host species. Host specific species resembled each other more than species associated with a broad range of hosts. Of the other selected ectomycorrhizal fungi, an isolate of Paxillus involutus collected from association with Corylus cornuta showed higher nitrate reductase activity than any of the other fungi collected which were from coniferous forests. These results support the concept that, for nursery inoculation mycorrhizal fungi must be carefully selected for specific sites and host species.
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