Submitted to: Mycopathologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 24, 2006
Publication Date: September 1, 2006
Citation: Pratt, R.G. 2006. Enhancement of sporulation in species of Bipolaris, Curvularia, Drechslera, and Exserohilum by growth on cellulose-containing substrates. Mycopathologica. 162:133-140. Interpretive Summary: Fungi are some of the main microorganisms that comprise the soil microbial community. This is a diverse array of microorganisms that exist in all soils at population levels of up to millions per gram. On swine and poultry waste application sites, where waste materials from swine and poultry production farms are disposed, soil fungi participate in activities that may either reduce or increase nutrient pollution of adjacent water that originates from these sites. To study the ecology of fungi in these soils, it is necessary for scientists to obtain large numbers of fungal spores. These are microscopic seeds of fungi that are produced in large numbers and enable their survival in soil. In this study, it was discovered that for nine species or related fungi that occur on animal waste application sites, growth on substrates that contain cellulose, a common material from plants, causes them to produce spores in far greater numbers than are produced on agar alone (the medium on which fungi are normally grown in the laboratory). Growth of the fungi on pieces of paper index card usually was most effective in increasing spore production, but increases also were observed after their growth on filter paper, cheesecloth, and cotton fabric. For most fungi, growth on one or more of these substrates stimulated them to produce large numbers of spores in concentrations adequate for studies on the survival of spores in soil. Four of the fungal species also were directly identified from soil of a swine waste application site when filter paper was placed directly onto plates to which dilutions of soil were added, after the fungi grew into the filter paper and produced spores upon it. Therefore, cellulose substrates can be used to increase production of spores of these fungi for experimental purposes, and also to enable their direct detection and identification from soil.
Technical Abstract: Nine species of Bipolaris, Curvularia, Drechslera, and Exserohilum were compared for sporulation on agar media and for enhancement of sporulation by growth on four cellulose substrates (index card, filter paper, cheesecloth, cotton fabric). On one natural and one synthetic agar medium, sporulation varied from profuse to nonexistent among three isolates of each species. Growth of all species on cellulose substrates resulted in large and significant increases in sporulation. Growth on index cards usually provided the greatest increases, but no single substrate was superior for all species, and significant substrate x isolate interactions were observed within species. Overlay of filter paper onto whole colonies in agar plates resulted in 2-18-fold increases in sporulation for eight of nine species and production of spores in sufficient quantity for most experimental purposes. Overlay of soil dilution plates with filter paper to promote sporulation of colonies enabled detection of B. spicifera, B. hawaiiensis, C. lunata, and E. rostratum at relatively low population levels (</=1.3 x 103 colony-forming units per gram) in samples of a naturally infested soil. Results of this study indicate that enhancement of sporulation by growth of species of Bipolaris, Curvularia, Drechslera, and Exserohilum on cellulose substrates may enable identification of isolates in culture, production of spores at relatively high concentrations, and detection of these fungi in soil and estimation of their population levels.