Scanning Electron Microscopy of Conidium Formation of Stemphylium vesicarium on Onion Leaves

Onion leaves were inoculated with conidia of Stemphylium vesicarium and the development and morphology of conidiophores and conidia on the leaf surface were examined using scanning electron microscopy. Solitary, but usually fasciculate conidiophores emerged through the epidermis. Hyphae growing on or above the leaf surface also differentiated into conidiophores. Conidiophores were straight or flexuous, simple, smooth or verrucose and cylindrical but enlarged apically at the site of conidiumproduction. Smooth, round, bud-like conidial initials were produced singly at the apex of the verrucose conidiophores. As conidia matured, they became oblong to ovoid and densely verrucose. Once the mature conidium seceded, a small pore was visible at the, apex of the conidiogenous cell. Conidiophores proliferated percurrently at the distal region, forming secondary conidiophores and conidia.