Systematics, biogeography and control of artillery fungi (Sphaerobolus spp.)

open_access
Open Access
Author:
Geml, József
Graduate Program:
Plant Pathology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 27, 2004
Committee Members:
David Michael Geiser, Committee Chair/Co-Chair
Donald Durwood Davis, Committee Chair/Co-Chair
Daniel J Royse, Committee Member
Elwin Lynn Stewart, Committee Member
S Blair Hedges, Committee Member
Keywords:
evolution
mycology
phylogenetics
Abstract:
Sphaerobolus is a basidiomycete with dual lignicolous and coprophilous ecology that is often found on landscape mulch. Mycologists have studied its spore dispersal mechanism, phototropism, and its possible control using biocontrol agents and different types of mulch. Virtually no research has been done, however, on the systematics, population structure, and chemical control of artillery fungi. Therefore, the goal was to elucidate the systematics of Sphaerobolus species using both molecular and morphological data, to obtain information about the biogeography of different species in the genus, and to investigate the effectiveness of various fungicides as candidates for control. Phylogenetic analyses of artillery fungi (Sphaerobolus spp.) isolates (n=26) were conducted to identify species boundaries in the genus Sphaerobolus. Multiple gene genealogies inferred from maximum likelihood, Bayesian and maximum-parsimony analyses of sequence data from individual loci (mtSSU, ITS, EF 1-a, and LSU) and a combined dataset (mtSSU, ITS, EF 1-a) concordantly indicate the existence of three deeply divergent lineages in the genus Sphaerobolus, each representing a phylogenetic species. These three phylogenetic species correspond to two known species: Sphaerobolus iowensis (n=12) and Sphaerobolus stellatus (n=10), and a newly discovered species, provisionally named Sphaerobolus ingoldii prov. sp. nov. (n=4). This latter species is going to be described in a separate publication. Suprageneric phylogenetic analyses of the mtSSU and LSU datasets containing representatives of related genera of the gomphoid-phalloid clade of homobasidiomycetes suggested the monophyly of the genus Sphaerobolus and that S. ingoldii prov. sp. nov. likely is more closely related to S. stellatus than to S. iowensis. Macro- and micro-morphological analyses of colony and basidiocarp characters confirmed that these three phylogenetic species correspond to two known species: S. iowensis and S. stellatus, and Sphaerobolus ingoldii prov. sp. nov. Species can be distinguished based on colony morphology and growth rate on agar media, and the composition and morphology of cells within the gleba. Despite the considerable amount of DNA polymorhism found in all species, nested clade analyses of S. iowensis and S. stellatus indicated little phylogeographic structure in either species. A very likely explanation is the extensive dispersal, due to the dual coprophilous and lignicolous ecology of Sphaerobolus species, that provides many possible dispersal scenarios over great geographic distances. However, statistically significant genotype-geography associations were detected in one clade of each species, suggesting restricted gene flow due to isolation by distance for some isolates. The inhibitory effect of 14 fungicides, 13 of which were known to be effective against the basidiomycete Agaricus, was tested at two concentrations (5 and 20 ppm) on the in vitro growth of three species of artillery fungi: S. iowensis, S. stellatus, and Sphaerobolus ingoldii prov. sp. nov. Opus®, Topsin M 70WP®, triphenyltin acetate, Difolatan®, and Terraguard 50W® were the most effective inhibitors of growth for all three Sphaerobolus species; reduction in growth was directly related to fungicide concentration. Five fungicides showed varying results, depending on fungal species and fungicide concentration. Four fungicides showed no significant inhibition on these artillery fungi. Although this preliminary study provided interesting results, potential fungicides must be tested in the field and registered by E.P.A. before recommendations can be made to homeowners who want to minimize adverse effects of artillery fungi.