Germination, penetration and sporulation of Cercospora henningsii (Allesch.) on cassava leaves were studied by scanning electron microscopy. Conidia started to germinate 9 h postinoculation producing one to two germ tubes. The germ tubes entered the leaf tissue through the abaxial surface by direct penetration of the epidermis without forming appressoria. The cassava leaf is characterized by its papillose epidermis on the abaxial surface. The penetrations occurred at smooth areas of the leaf epidermis between the papillae. The germ tubes did not enter stomata even when they passed over stomatal openings. Leaf spots started to appear 9 days after the inoculation (dpi), and the emergence of conidia occurred 14 dpi. The symptoms appeared first on the abaxial leaf surface, followed 2 days later on the adaxial. Conidia emerged in clusters through ruptured epidermis on both sides of the leaves. Conidia emerged also through the epidermal papillae and the leaf veins. Even though small groups of conidia emerged through stomata also, emergence through stomata appeared to be random rather than a preferred route. Each conidium was born on a short conidiophore with a swollen base.

White muscardine is a common disease of the silkworm Bombyx mori caused by an insect mycopathogen Beauveria bassiana. The present study revealed the germination, penetration, and invasion of B. bassiana on the larval integument of B. mori. The NB 18 strain of B. mori was surface inoculated with concentrations of 1×10 6 conidia/ml. Each conidium, germinated approximately 8 h after inoculation, forming an appressorium within 24 h and the hypha entered the cuticle by forming a clear circular hole. The hyphae reached the haemocoel, where they grew and multiplied extensively, forming a mycelial complex, causing death of the host larva in about five-six days. This occurred with minimal breakdown of the internal tissues. Death of the host was followed by ramification of the fungus through the mesodermal and epidermal tissues, leading to larval mummification about six days post-inoculation. Extensive fungal outgrowths followed, mostly through the intersegmental regions of the larva, and formed aerial hyphae, which gave rise to branched conidiophores forming a confluent white fungal mat over the entire larval body in six-seven days. The life-cycle of the fungus on B. mori was completed in seven-eight days.KEY WORDS: Bombyx mori -Beauveria bassiana -White muscardine -Silkworm disease. ACKNOWLEDGEMENTS

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Unicelled conidia of Colletotrichum gloeosporioides germinated 3 h after inoculation producing single germ tubes. The orientation of the germ tubes and their lateral branches as they grew was towards the open stomata and away from closed stomata. By 24 h post-inoculation, the lateral branches had developed specialized infection vesicles either over the stomata or within the stomatal cavities. The infection vesicles produced primary infection hyphae which entered the leaves through stomatal openings. The disease symptoms became apparent by 6 days post-inoculation when clusters of abundant conidiophores emerged by rupturing the leaf epidermal layer, forming acervuli mostly near the base of idioblasts. The pressure exerted by the emerging conidiophores caused stretching of epidermal layer leading to the widening of the acervuli. The conidia are borne on the tips of the erect conidiophores. U. S. Copyright Clearance Center Code Statement: 0931±1785/2001/4912±0629 $ 15.00/0 www.blackwell.de/synergy 630 KUMAR UMAR et al.

Structure and development of Cercospora ricinella, the causal agent of the castor leaf spot, were studied by scanning electron microscopy. The conidia started to germinate 9 h post inoculation, producing an appressorium directly from the tip of conidium or at the end of a short germ tube. A single germ tube or appressorium was formed from the apical cell of each germinating conidium. Germ tubes or appressoria did not grow towards stomata, and penetration of the leaf appeared to be by piercing the epidermis. Leaf spots appeared 7 days post inoculation (dpi), and after approximately 12 dpi, clusters of two to many conidia emerged from both surfaces of the leaf through the epidermis or through stomatal openings. Stomata were torn when a large number of conidia emerged through them, and conidia also pierced the epidermis above the guard cells of stomata. Emergence through stomata appeared to be random rather than a preference.

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Aspergillosis is a common disease of the silkworm Bombyx mori Linn., caused by an insect mycopathogen Aspergillus flavus Link:Fries. The present study reveals the germination, penetration and conidial development of A. flavus on the larval integument of B. mori under SEM. Four different strains (NB18, KA, NB4D2 and NB7) of B. mori was surface inoculated with ca. of 1 x 10(6) conidia/ml. Each conidium germinated on the cuticle approximately 6 h after inoculation, forming a humpy or suctorial appressoria within 24 h. The hyphae which entered into haemocoel 2 day post-inoculation, grew and multiplied extensively, forming a mycelial complex, causing death of the host larva in about 4-5 days. This occurred with minimal breakdown of the internal tissues. Death of the host was followed by ramification of the fungus through the mesodermal and epidermal tissues, leading to larval mummification about 5-6 days after inoculation. Extensive fungal growths on the entire larval body followed, consisting of aerial hyphae, which developed branched conidiophores. The aerial hyphae with abundant conidiophores formed a confluent yellowish green fungal mat over the entire larval body in 6-7 days of post-inoculation. The tip of each emerging conidiophores gradually dilated and developed to become a bulbous head known as the vesicle. A large number of conidiogenous cells were produced over the entire surface of vesicle, which later developed into finger-like projections termed as sterigmata or phialides. The phialides matured within 2 days after the aerial hyphae emerged as evidenced by chains of conidia at their tips. The conidia were globose with externally roughened walls. The life cycle of the fungus on B. mori was completed in six to seven days.

The pith ducts of Ailanthus excelsa Roxb. (Simaroubaceae) secrete gum-resin. The synthesis of resin in the epithelial cells of the duct is associated with plastids and endoplasmic reticulum (ER) while dictyosomes are involved in the synthesis of the gum. In the secreting cells, large numbers of osmiophilic globules are scattered in the cytoplasm. Dictyosomes and ER produce abundant vesicles. The osmiophilic globules and vesicles fuse with the plasmalemma facing the duct lumen and are entrapped in plasmalemma invaginations. The walls of some of the epithelial cells have a few ingrowths which presumably enhance the efficiency of the cell in the transportation of materials from the cytoplasm. Some of the epithelial cells in a duct undergo autolysis and degeneration after secretion. The appearance of autophagic vacuoles containing portions of cytoplasm, the loss of tonoplast, the distortion of ER, mitochondria, dictyosomes and the darkening of cytoplasm are some of the autolytic features in the degenerating cells. The lysed cells with 'dark' cytoplasm, osmiophilic droplets and free ribosomes detach and disintegrate in the duct lumen, becoming part of the gum-resin content in the duct.