SHORT NOTE Reducing airborne ectomycorrhizal fungi and growing non-mycorrhizal loblolly pine (Pinus taeda L.) seedlings in a greenhouse Aaron D. Stottlemyer & G. Geoff Wang & Christina E. Wells & David W. Stottlemyer & Thomas A. Waldrop Received: 6 September 2007 / Accepted: 9 April 2008 / Published online: 15 May 2008 # Springer-Verlag 2008 Abstract Atmospheric spores of ectomycorrhizal (ECM) fungi are a potential source of contamination when mycorrhizal studies are performed in the greenhouse, and techniques for minimizing such contamination have rarely been tested. We grew loblolly pine (Pinus taeda L.) from seed in a greenhouse and inside a high-efficiency particu- late air-filtered chamber (HFC) constructed within the same greenhouse. Seedlings were germinated in seven different sand- or soil-based and artificially based growth media. Seedlings grown in the HFC had fewer mycorrhizal short roots than those grown in the open greenhouse atmosphere. Furthermore, the proportion of seedlings from the HFC that were completely non-mycorrhizal was higher than that of seedlings from the greenhouse atmosphere. Seedlings grown in sterilized, artificially based growth media (>50% peat moss, vermiculite, and/or perlite by volume) had fewer mycorrhizal short roots than those grown in sand- or soil-based media. The HFC described here can minimize undesirable ECM coloni- zation of host seedlings in greenhouse bioassays. In addition, the number of non-mycorrhizal seedlings can be maximized when the HFC is used in combination with artificially based growth media. Keywords Ectomycorrhizas . Soil inoculum potential . Bioassays . Greenhouse Introduction Mycorrhizal studies that are performed in greenhouses include bioassays of soil inoculum potential (Herr et al. 1994; Teste et al. 2006), assessments of mycorrhizal community structure (Jones et al. 2003; Pilz and Perry 1984), and experimental inoculation with specific ectomycorrhizal (ECM) fungal symbionts (Beckjord and McIntosh 1983; Branzanti et al. 1999; Brundrett et al. 1996; Marx and Bryan 1969). There are two primary methods of assessing soil inoculum potential or mycorrhizal community structure. The first involves obtaining field soil, diluting it with different concentrations of sterile soil or a soilless medium (‘most probable number’ assay—see Brundrett et al. 1996) or obtaining intact soil cores and planting ECM host seed in the soil (Boerner et al. 1996). The second method involves producing non- mycorrhizal seedlings of an ECM host species and planting the seedlings in diluted soil (Brundrett et al. 1996) or intact soil cores (Smith et al. 1995), or outplanting the seedlings in undisturbed field soil (Tainter and Walstad 1977). In both cases, the ‘trap plants’ are left to grow for a period of time, then excavated and assessed for mycorrhizal colonization. However, aerial ECM fungal spores are a potential source of contamination when these tasks are performed in Mycorrhiza (2008) 18:269–275 DOI 10.1007/s00572-008-0176-3 A. D. Stottlemyer : G. G. Wang (*) Department of Forestry and Natural Resources, Clemson University, Clemson, SC 29634-0317, USA e-mail: gwang@clemson.edu C. E. Wells Department of Horticulture, Clemson University, Clemson, SC 29634-0317, USA D. W. Stottlemyer RamTech, Inc., Chambersburg, PA 17201-1450, USA T. A. Waldrop USDA Forest Service, Southern Research Station, Clemson, SC 29634-0317, USA