Biomechanics of Rhizomorph Development in Armillaria mellea

 
 
 
 

Biomechanics of Rhizomorph Development in Armillaria mellea

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Title: Biomechanics of Rhizomorph Development in Armillaria mellea
Author: Yafetto, Levi
Description: Fungal rhizomorphs are complex, multicellular, root-like organs formed through the aggregation, interlacing, and adhesion of millions of tip-growing hyphae. There has been very little research on the invasive mechanism utilized by rhizomorphs to penetrate compacted soils and woody substrates. Initial studies with Meruliporia incrassata, a wood-decay fungus that decomposes wooden components of buildings with an annual value of destruction estimated in millions of dollars, was aimed at inducing rhizomorphs in vitro. This attempt was not very successful, as only mycelial cords were produced. The pathogen Armillaria mellea was therefore chosen because it readily forms rhizomorphs in culture and serves as an excellent model for developmental studies. This dissertation presents findings from experiments designed to study (i) comparative features of rhizomorph anatomy in M. incrassata and A. mellea that support its invasive behavior; (ii) the adaptive growth response of rhizomorphs subjected to mechanical stress; (iii) the biochemical basis of turgor generation within rhizomorphs, and (iv) novel measurements of the forces exerted by growing rhizomorphs. Anatomical studies of rhizomorphs of A. mellea cultured in potato dextrose agar (PDA) revealed zones of hyphal tissues namely, an outer layer of peripheral hyphae, radial hyphae, longitudinal hyphae, and a central cavity. A. mellea rhizomorphs were observed to have faster growth than mycelia in PDA. We determined that increasing concentration of agar stimulated the production of more rhizomorphs, with those in media having higher concentration of agar extending faster with tapered tips. Turgor generation within A. mellea rhizomorphs was shown to be partially due to the accumulation of osmolytes. Erythritol and mannitol were identified using Gas Chromatography/Mass Spectrometry (GC/MS) and quantitatively determined to be the most dominant osmolytes that contribute to turgor generation. Osmometric studies revealed that substantial portion of turgor generated was used to exert pressure at the tip of the rhizomorphs during invasive growth. The varying amounts of force that these A. mellea rhizomorph tips exert were measured, using a sensitive strain gauge. Our experiments provide the first clear picture of the mechanical processes that allow rhizomorphs to function as migratory, exploratory and invasive organs in low-moisture and nutrient-poor environments that present substantial obstacles to fungal colonization.
Permanent Link: http://rave.ohiolink.edu/etdc/view?acc_num=miami1217948884
http://hdl.handle.net/2374.OX/108487
Date: 2008

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