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Mycelium development and architecture, and spore production of Scutellospora reticulata in monoxenic culture with Ri T-DNA transformed carrot roots

     Embrapa Agrobiologia, Caixa Postal 74505, CEP 23851-970, Seropédica, RJ, Brazil Department of Plant Microorganism Interaction

Stéphane Declerck

     Université catholique de Louvain, Mycothèque de l'Université catholique de Louvain², Unité de microbiologie, 3 Place Croix du Sud, 1348 Louvain-la-Neuve, Belgium

Mycelium development and architecture and spore production were studied in Scutellospora reticulata from single-spore isolates grown with Ri T-DNA transformed carrot root-organ culture in monoxenic system. Culture establishment, anastomosis occurrence and auxiliary cell development also were examined. Seventy percent of the pregerminated disinfected spores colonized the transformed carrot roots. After 8 mo, the average spore production was 56 (24–130) per 30 cm³ of medium. Of the spores produced, 75% germinated and produced new generations in monoxenic culture. The mycelium network was formed by thick light-brown hyphae, which exhibit two major architecture patterns related to either root colonization or resource exploitation, and lower-order hyphae, bearing auxiliary cells, branched absorbing structures (BAS), hyphal swellings (HS) and forming anastomoses. BAS were formed abundantly in extramatrical mycelium and frequently had HS resembling vesicles, a feature not previously reported in the Gigasporaceae, to the best of our knowledge. Few anastomosis were observed within the mycelium and most often corresponded to a healing mechanism that form hypha bridges to reconnect broken hyphae or overcoming obstructed areas within a hypha. Numerous auxiliary cells were produced during culture development and their role was inferred.

Key words: anastomosis, arbuscular mycorrhizal fungi, auxiliary cell, branched absorbing structures, Gigasporaceae, Glomeromycota, hyphal swelling, monoxenic culture