Fungal Morphogenesis Tracking of Blumeria graminis f. sp. tritici on Leaf Freed of Epicuticular Wax Using Scanning Electron Microscopy

Abstract

Fungal morphogenesis development of Blumeria graminis f. sp. tritici was tracked on leaves freed of epicuticular wax using the scanning electron microscopy during successive times, 1 day post inoculation (dpi), 2 dpi, 3 dpi, 4 dpi, 5 dpi and 7 dpi. A conidium seen 1 dpi landing on a leaf showed spore germination and the presence of primary germ tube and the appressria formation revealing their dimensions. Appressorial germ tube has elongated and swollen to form an infection structure, the appressorium has a hooked apical lobe. At 2 dpi, the network of tubular cells forms the mycelial hyphae growing over the leaf surface being fed by a haustorium hidden inside the cell under the appresorium. By 3 dpi, colony consisted of mycelial hyphae with rare hyphal lobes. Appressorial lobes tightly adhered to the surface of epidermal cells. At 4 dpi, extensive hyphal growth and repeated penetration from hyphal appressoria resulted in the formation of further haustoria and bulbous conidiophores. On 5 dpi, bulbous conidiophores have started generating conidia. By 7 dpi, well-developed fungal colony were formed with many chains of conidia sticking up into the air and can be wind spread to initiate new infection cycles. We cannot be sure that removing of the waxes did not affect the pathogen's ability to produce conidial exudates or extracellular material from its germ tubes, appressoria, or hyphae. However, we believe this is unlikely, since removing of leaf waxes prior to inoculation has very little effect on many different aspects of fungal development.