SCANNING ELECTRON-MICROSCOPY OF CONIDIUM FORMATION OF STEMPHYLIUM-VESICARIUM ON ONION LEAVES

Onion leaves were inoculated with conidia of Stemphylium vesicarium an d the development and morphology of conidiophores and conidia on the l eaf 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 con idium production. Smooth, round, bud-like conidial initials were produ ced singly at the apex of the verrucose conidiophores. As conidia matu red, they became oblong to ovoid and densely verrucose. Once the matur e conidium seceded, a small pore was visible at the apex of the conidi ogenous cell. Conidiophores proliferated percurrently at the distal re gion, forming secondary conidiophores and conidia.