FRACTAL GEOMETRY OF DIFFUSE MYCELIA AND RHIZOMORPHS OF ARMILLARIA SPECIES

Fractal geometry was used to quantify the variation in branching patte rns of sibling basidiospore-derived diffuse mycelia of Armillaria gall ica and rhizomorph systems of A. gallica and A. ostoyae in laboratory culture. The fractal dimension (D) of II A. gallica diffuse mycelia ra nged from 1.05 to 1.20 at 74 h after basidiospore germination, and fro m 1.43 to 1.57 at 116 h after germination. The coefficient of variatio n (CV) for the regression coefficients of D on time was 14.8%, whereas the CV for D of all II mycelia at the fourth measured time step was o nly 2.9%, indicating significant convergence towards a given branching pattern for a particular set of environmental conditions. The rhizomo rph systems of diploid A. gallica thalli branched more profusely than those of diploid A. ostoyae. D values among replicate rhizomorph syste ms for strains representing three A. gallica genets were similar, wher eas rhizomorph systems of eight of the 12 A. ostoyae thalli, also repr esenting three genets, either failed to develop or did not branch suff iciently to permit calculation of D. D values of rhizomorph systems we re generally temporally invariate for both species. The CV of D for re plicate rhizomorph systems at the fourth measured time step was betwee n 1.6% and 3.9% for A. gallica genets and 2.4% for the A. ostoyae gene t; D was significantly lower for the A. ostoyae genet than for the thr ee A. gallica genets. A. gallica is only weakly pathogenic and can col onize a taxonomically broad range of food bases saprotrophically. A. o stoyae is more pathogenic and colonizes a narrower range of substrata. The profuse rhizomorph branching pattern of A. gallica is consistent with a foraging strategy in which acceptable food bases may be encount ered at any distance, and which favours broad and divisive distributio n of potential inoculum. The sparse branching pattern of A. ostoyae rh izomorph systems is less divisive, consistent with the conservation of nutrients necessary to maintain rhizomorph inoculum potential more ef ficiently with increasing distance from a foodbase.