Sclerotial morphogenesis in Sclerotium cepivorum in vitro

Abstract

LITTLEY, E. R., and RAHE, J. E. 1992. Sclerotial morphogenesis in Sclerotiurn cepivorum in vitro. . Sclerotial ontogeny, maturation, and aging in Sclerotium cepivorum are described using light and scanning electron microscopy. On potato dextrose agar, the mycelium spread, branching irregularly. Six days after inoculation sclerotial initials appeared, formed by hyphae branching and looping. From 6 to 8 days, the number and size of initials increased, and mucilagenous material appeared. By day 9, hyphal bundles formed in the mycelium. Between 9 and 11 days, spherical forms developed and the sclerotia grew. By day 12, an acellular matrix appeared, and to day 18 this matrix progressively obscured the surface hyphae and became black. A layer of ovoid rind cells developed at the surface. To examine the reduced survival of laboratory-produced compared with field-collected sclerotia, sclerotia from a variety of sources and conditions were compared. In general, the rind of sclerotia aged in dry conditions had a broken, irregular appearance versus fresh sclerotia or sclerotia aged under moist, axenic conditions. Sclerotia aged dry developed 1 to 4 layers of rind cells, while sclerotia kept moist developed only 1 or 2 layers. The structural and survival differences between laboratory-produced and natural sclerotia are attributable to differences in the moisture conditions under which they matured and aged. LITTLEY, E. R., et RAHE, J. E. 1992. Sclerotial morphogenesis in Sclerotium cepivorum in vitro. Can. J . Bot. 70 : 772-778. Les auteurs dtcrivent l'ontogtnbse, la maturation et le vieillissement du Sclerotium cepivorum i I'aide de la microscopie tlectronique par balayage. Sur extrait de pomme de terre gtloste, le myctlium s'ttend en se ramifiant irrtgulikrement. Six jours aprbs l'inoculation les primordia des scltrotes apparaissent et se forment par ramification et enroulement des hyphes. Des jours 6 i 8, le nombre et la grosseur des primordia augmente et du mattriel mucilagineux apparait. Vers le 9ibme jour, des faisceaux d'hyphes se forment dans le myctlium. Entre les jours 9 et 11, la forme sphtrique apparait et le scltrote grossi. Vers le l2ibme jour, une matrice acellulaire prend forme et jusqu'au 18ibme jour cette matrice obscursi progressivement les hyphes de surface et se mtlanise. Une couche de cellules corticales ovo'ides se dtveloppe i la surface. Afin de determiner la rtduction de la survie de scltrotes produits au laboratoire comparativement i des sclCrotes produits aux champs, les auteurs ont compare des scltrotes d'origines et de conditions diverses. En gtntral, les cortex des scltrotes vieillis sous des conditions skches montrent une apparence briste et irrtgulibre, contrairement aux scltrotes frais ou vieillis i I'humiditt en conditions axtniques. Les scltrotes vieillis au sec montrent un i quatre couches de cellules corticales alors que ceux qui le sont i l'humiditt n'en comportent que un ou deux couches. Les differences dans les structures et dans la survie entre les scltrotes produits au laboratoire et...

Deletion of the Delta12-oleic acid desaturase gene of a nonaflatoxigenic Aspergillus parasiticus field isolate affects conidiation and sclerotial development

“…Aspergillus parasiticus is a strictly mitotic (asexual) species. Deletion of the odeA gene likely affects fatty acid composition and the ratio of saturated to unsaturated fatty acids of ΔodeA mycelia and, in turn, alters the timing and frequency of appearance of sclerotial initials and maturation of sclerotia (Littley and Rahe 1992; Willetts and Bullock 1992). Loss of odeA would also alter the composition of PSI factor, which we predict would affect the conidia to sclerotia ratio.…”