Development of the Leaf Spot Fungus, Cercospora ricinella, on Castor Leaf – an SEM Account

Abstract

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.

Germination, penetration and sporulation ofAlternaria ricini(Yoshii) Hansf. on castor leaf

“…Conidiophores emerged by piercing or rupturing epidermal cells over stomatal complex when there was no emergence through that stomatal opening. A similar observation was found with C. ricinella on castor leaf (Babu et al 2007) indicating that the emergence of conidia through stomata was at random, rather than a preferred route, and that Figure 8 shows the emergence of three conidia from a stoma. Note the cushion-shaped base (arrowhead) of conidiophore (cp).…”

“…As observed in Cercospora ricinella on castor leaf (Babu et al 2007), the conidia were released through stomata as well as through ruptured epidermis apparently without any preference for the emergence route. Conidiophores emerged by piercing or rupturing epidermal cells over stomatal complex when there was no emergence through that stomatal opening.…”

“…In P. mori the discharge of conidia was solely through stomata as the stromata inside the leaf tissue were always oriented below stomata for the release of conidia. In C. ricinella (Babu et al 2007) the emergence of abundant conidia caused the tearing of stomata, whereas the stomata on the blight-infected castor leaves were intact as only 1 -3 conidiophores of A. ricini emerged through a stoma at a time. On epidermal cells also, the conidiophores of A. ricini emerged solitarily or in small clusters of 2 -4, whereas the conidia of C. ricinella emerged in clusters of abundant numbers.…”

Microscopia eletrônica de varredura do processo infeccioso de Ramularia areola em folhas de algodoeiro

“…Resultados semelhantes foram observados para Ramularia sphaeroidea em Vicia sp. (Koike et al, 2004) e C. ricinella em folhas de mamona (Babu et al, 2007). Observou-se uma grande quantidade de hifas de R. areola colonizando inter e intracelularmente o mesófilo foliar (Figura 2f) a semelhança do que foi relatado para R. collo-cygni em cevada (Stabentheiner tabentheiner et al, 2009).…”

“…Essa grande quantidade de tubos germinativos foi atribuída ao fenômeno denominado de confusão trópica, que nada mais é do que um mecanismo de resistência do hospedeiro para impedir a penetração do patógeno (Wynn, 1981). Babu et al (2007Babu et al ( , 2009, estudando os patossistemas mamona -Cercospora ricinella e mandioca -Cercospora henningsii também não observaram direcionamento dos tubos germinativos dos conídios dessas duas espécies de Cercospora para o interior dos estômatos presentes na superfície adaxial das folhas dos seus hospedeiros.…”