Studies on the powdery mildew fungus Sphaerotheca fuliginosa on squash in Egypt: ultrastructure and some physiological host responses

ABSTRACT

According to the criteria of conidia and cleistothecia, this study revealed that, the powdery mildew fungus which infects squash in Nile Delta, Egypt is Sphaerotheca fuliginea. This fungus was studied by light microscopy, scanning and transmission EM. The conidia are barrel or oval-shaped with wrinkled surface. The cleistothecia are spherical and contain one ellipsoid to spherical ascus with 4-8 ellipsoid ascospores. The host epidermal cell was penetrated by a penetration peg which, after penetration developed into haustorium consisting of a nucleated central body with several lobes, embedded in a matrix. The surrounding extrahaustorial membrane is an invagination of the plasmalemma of the host cell. As a defence mechanism, a collar was formed arround the penetration peg. Chloroplasts of infected leaf of squash showed a dramatic changes in their utltrastructure. The infection caused an alteration in the physiology of squash leaf. It is obvious that there wig a marked depletion in reducing sugars and sucrose which- accompanied by a simultaneous elevationn in polysaccharides of infected leaœ Also, the pigment content [chlorophyll. a,b and carotenoids] appeared geared to be reduced as a result of such infection. There was a massive decrease in the endogenous growth stimulants levels [auxins, gibberellins and cytokinins] with a concomitant increase in growth inhibitors in infected leaf of squash