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 pr oduce spores singly in soil. Glomus eburneum spores are hyaline or white to cream, usually irregular (40 x 60 to 140 x 160 mu m diam) and more rarely globose (40-140 mu m diam). The spore wall consists of two adherent permane nt hyaline layers, neither of which reacts in Melter's reagent. The outer l ayer is thin (<1.2 mu m), and the inner layer is finely laminate. Spores of G. luteum are globose to subglobose, 60-180 mu m diam and pale yellow to d ark yellow with a brownish tint. The spore wall consists of four layers, th e two outer layers often degrading at maturity. The outer layer is mucilagi nous and stains pinkish-red in Melzer's reagent. The second layer is hyalin e and semirigid. Rigid, pale yellow to brownish yellow laminae comprise the third layer. Mature spores exhibit a fourth layer that is thin, flexible a nd may separate from the laminate layer under pressure. Both species were i dentified from pot cultures established with soil and root fragments from a semiarid giant sacaton (Sporobolus wrightii) grassland and subsequently cu ltured on sudangrass, Sorghum sudanense. Both species formed arbuscular myc orrhizae in pot cultures with corn (Zea mays) as the host.