Histological Investigations on Infection of Grape Roots and Shoots by «Phaeoacremonium» spp.

Abstract

Tissue-cultured grapevines cv. Cabernet Sauvignon were used to determine whether injury is a prerequisite to penetration of shoot and root tissue by Phaeoacremonium spp. and to ascertain the path of invasion inside the host. Uninjured and injured roots and shoots were inoculated with P. inflatipes and P. aleophilum at approximately 106 spores ml-1. Isolation and scanning electron microscopy observations showed that Phaeoacremonium spp. was capable of penetrating uninjured roots and shoots. Light microscopy observations of paraffin embedded sections showed that rapid spread of the fungus in roots was through the vascular tissues and intercellular spaces of the cortex. In the shoots, spread of the fungus was initially through the intercellular spaces of the epidermis, cortex, and pith; rapid spread apparently occurred in the intercellular spaces of the pith. Spores were seen in the pith area as well as in the xylem. Remote from the point of inoculation, hyphae were seen in the epidermis, cortex, pith, and vascular tissues without noticeable change in appearance of the invaded cells. Symptoms of the disease were observed in some plants 2 months after inoculation but isolations made in symptomless plants after 2 weeks showed the presence of the fungus in all parts of the plant.