Glomus eburneum and G. luteum, two new species of arbuscular mycorrhizal fungi, with emendation of G. spurcum

Two species of arbuscular mycorrhizal fungi, Glomus eburneum and G. luteum, are described and the description of G. spurcum is emended. All species produce spores singly in soil. Glomus eburneum spores are hyaline or white to cream, usually irregular (40 X 60 to 140 X 160 μm diam) and more rarely globose (40-140 μm diam). The spore wall consists of two adherent permanent hyaline layers, neither of which reacts in Melzer's reagent. The outer layer is thin (<1.2 μm), and the inner layer is finely laminate. Spores of G. luteum are globose to subglobose, 60-180 μm diam and pale yellow to dark yellow with a brownish tint. The spore wall consists of four layers, the two outer layers often degrading at maturity. The outer layer is mucilaginous and stains pinkish-red in Melzer's reagent. The second layer is hyaline and semirigid. Rigid, pale yellow to brownish yellow laminae comprise the third layer. Mature spores exhibit a fourth layer that is thin, flexible and may separate from the laminate layer under pressure. Both species were identified from pot cultures established with soil and root fragments from a semiarid giant sacaton (Sporobolus wrightii) grassland and subsequently cultured on sudangrass, Sorghum sudanense. Both species formed arbuscular mycorrhizae in pot cultures with corn (Zea mays) as the host.