Evidência electrono-microscópica de multiplicação dos vírus do mosaico do fumo e de vira-cabeça, em tecido foliar de cafeeiro

Abstract

Coffea plants (Coffea arabica L.) may be infected with vira-cabeça (Brazilian tomato spotted wilt) or tobacco mosaic (TMV) viruses, by mechanical means. Vira-cabeça virus (VCV) induces on leaves of ino- culated plants, chlorotic spots, resembling ringspot, while a virulent isolate of TMV causes chlorotic lesions with a necrotic center. In both cases, the viruses did not become systemic. Thin section profiles of leaf tissues obtained from the lesions caused by TMV or VCV were examined in the electron microscope. In cells from chlorotic lesions of TMV-inoculated coffea leaves, many cytoplasmic inclusions, with a fibrous aspect, were found. These inclusions were observed in epidermal, spongy and palisade parenchyma, but not in the vascular region. The rod-like particles, components of the inclusion are considered as TMV in situ. The fibrous inclusions were still identifiable, even in completely necrotic cells. X-body-like inclusions on the other hand, could not be seen. In cells from the lesion induced by VCV, spheroidal particles, iden- tified as those of the inoculated virus, were found mostly in epidermal cell. The particles were always within the endoplasmic reticulum elements. The finding of a large number of virus particles, in foliar tissue of coffea, infected by TMV or VCV, is considered as an evidence for the multiplication of these virus in the inoculated tissue, and supports previous pathological observations.