Histopathology of infection and colonisation of Elsinoë ampelina on grapevine leaves

Abstract

Elsinoe ampelina, the causal agent of grapevine anthracnose, infects all aboveground succulent parts of the plant, causing serious yield losses. There are no histopathological reports on this pathogen interaction with grapevine tissues. This study aimed at understanding the infection and colonisation processes of E. ampelina on Vitis labrusca cv. Niagara Rosada leaves by light, transmission and scanning microscopy. From one to five germ tubes per conidia were formed during conidia germination, predominantly one or two. Cuticle degradation was observed on plant surface underneath germ tubes and appressorium-like structures were rare. Monilioid and branched hyphae were observed 48 h post inoculation. Direct penetration occurred only on the adaxial leaf surface due to high trichome density on the abaxial leaf surface and conidia trapped on trichomes were frequently observed. The colonisation process was similar in the leaf blade, veins and petiole with the formation of inter- and intracellular hyphae. Phenolic compounds accumulated in infected areas; however, they did not prevent the colonisation progress. Tissues of foliar blade were totally changed by cell collapse and conidiogenous cells were observed on the surface of necrotic lesions. Ascus-like structures were observed within deeply unstructured tissues of leaf veins and necrotic areas of the petiole.