Root Colonization Pattern of Glomus Epigaeum in Nine Host Species

Abstract

Typically, vesicular-arbuscular mycorrhizae (VAM) can be distinguished in mature pot cultures of Glomus epigaeum Daniels & Trappe [=Glomus versiforme (Daniels & Trappe) Berch] (older than 1 yr) (Daniels and Trappe, 1979) by staining in Trypan blue/lactophenol (Phillips and Hayman, 1970). In experiments of 3-5 months, however, root colonization frequently has been difficult or impossible to discern even where positive growth responses occurred (Daniels and Menge, 1981; Hetrick, unpublished). Though degree of root colonization is not well correlated with growth response (Mosse, 1972; Graham et al, 1982), some minimal level of root colonization must occur if growth responses are to be explained by or at? tributed to mycorrhizae. Thus, the failure to distinguish colonization by G. epi? gaeum in young plants has made it difficult to interpret results of research with this fungus. This study explores whether staining characteristics, pattern and morphology of mycorrhiza development differ among host species. Per cent colonization and morphology of nine hosts were compared: honey locust (Gleditsia triacanthos L.), black locust (Robinia pseudoacacia L.), Kentucky coffeetree (Gymnocladus dioica L.), cotton (Gossypium hirsutum L.), soybean (Glycine max L. var. Essex), asparagus (Asparagus officinalis L. var. Mary Wash? ington), sudan grass [Sorghum sudanese (Piper) Staph.], corn (Zea mays L. var. O's Gold SX5500A), and tomato (Lycopersicon esculentum Mill. var. Tiny Tom). Seeds of black locust, honey locust, and Kentucky coffeetree were scarified in concentrated sulfuric acid for xh, 1 Vi, and 3 h, respectively, then rinsed in distilled water and allowed to germinate in steamed vermiculite. At various intervals thereafter, depending on germination time, the remaining hosts were planted in steamed vermiculite. When all seeds had germinated, nine replicate seedlings of each host were transplanted into 4x21 cm tubes (Ray Leach Cone-tainer Nursery, Canby, OR 97019) containing 165 g autoclaved 1:1 sand:soil mix. Inoculum of G. epigaeum was prepared by blending sporocarps in water until spores were dispersed (Daniels and Menge, 1981). Spores were counted using an eelworm counting cell (Daniels and Menge, 1981) and 200 spores in 5 ml water were pipetted onto the roots of each host plant as it was transplanted. Tubes were randomized to avoid shading effects on shorter hosts, and grown under sodium vapor lights in a 18-22 C greenhouse. Each host plant received 9.26 mg Peter's No-Phos Special (20-0-20) (A. H. Hummert Seed Co., St. Louis, MO 63103) fertilizer every 2 wk. After 8 wk, roots of each plant were washed, cleared in 10% KOH, stained in Trypan blue (Phillips and Hayman, 1970) and per cent coloni? zation (number of mm2 sections containing mycorrhizae) was determined on a