Glomus claroideum, an arbuscular mycorrhizal fungus new to Ireland, and its distribution in an Irish tree nursery

The arbuscular mycorrhizal (AM) populations in fumigated soil and AM coloni sation of ash and sycamore were investigated in the main bare-root nursery in Ireland. Only one AM spore type was found in the soil. This was identifi ed as Glomus claroideum (Walker and Vestburg 1998) and a single-spore cultu re has been lodged as BEG 62. In a sand/pot study using the single-spore cu lture as inoculum, both ash and sycamore showed no growth response to inocu lation. Ash seedlings had 25% AM infection, which was characterised by abun dant arbuscules, hyphae and occasional hyphal coils, but no AM infection oc curred in sycamore. In the nursery, chlamydospores of G. clairoideum increa sed in the soil between June-December, but there was a greater AM infectivi ty estimate based on the 'most probable number test compared with AM spore counts. Ash seedlings had an AM colonisation ranging 10-35%, whereas sycamo re was sparsely mycorrhizal (<2%). There was positive con-elation between s pore numbers of G. claroideum and AM. colonisation of ash growing in one pa rt of the nursery converted from agricultural land but not in another, whic h had been cleared of forest.