Douds Jr., D.D., USDA-ARS ERRC, 600 E. Mermaid Lane, Wyndmoor, PA 19038, United States
Galvez, L., USDA-ARS ERRC, 600 E. Mermaid Lane, Wyndmoor, PA 19038, United States
Bécard, G., Lab. de Mycologie Veg., Univ. Paul Sabatier, Bât. 4R1, 118 Route de Narbonne, 31062 Toulouse, France
Kapulnik, Y., Institute of Field and Garden Crops, P.O. Box 6, Bet Dagan, 50250, Israel

Two cvs of alfalfa (Medicago satira L.), Gilboa and Moapa 69, were inoculated in glasshouse pots with three arbuscular mycorrhizal (AM) fungi to investigate the efficacy of mycorrhizas with respect to the extent of colonization and sporulation. Paspalum notatum Flugge also was inoculated to describe fungai parameters on a routine pot culture host. Percentage root length of P. notatum colonized by Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe, Glomus intraradices Schenck and Smith, and Gigaspora margarita Becker and Hall increased from 10 to 21 wk, and all fungi sporulated during that period. In alfalfa, only colonization by G. intraradices increased over that time period, and it was the only fungus to sporulate in association with alfalfa at 10 wk. Glomus mosseae did not sporulate after 16-21 wk despite having colonized 30-35 % of the root length of both alfalfa cvs. In vitro experiments in which Ri T-DNA-transformed roots of alfalfa were inoculated with AM fungi showed normal mycorrhizal formation by G. intraradices and a hypersensitivity-like response to G. margarita. Colonized cells became necrotic, and HPLC analysis indicated increased concentrations of phenolics and isoflavonoids in these root segments. These data strongly support the existence of a degree of specificity between AM fungi and host that might rely on specific biochemical regulatory processes initiated in the host as a result of the attempts at colonization by the fungus.