STUDIES ON THE RELATIONSHIP BETWEEN VENTU RIA-INAEQUALIS AND MALUS X DOMESTICA IN VITROPLANTS

A simple and effective method for the infection of Malus x domestica p lantlets by apple scab [Venturia inaequalis] is described. Disease dev elopment was followed by macroscopic observation of symptoms and scann ing electron microscopy observations. The infection of rooted and micr opropagated plantlets of the susceptible cultivar Gala showed that roo ting is a necessary precondition for the establishment of the host-pat hogen relationship. On the nonrooted plantlets, there was no disease e xpression; hyphae remained over the leaf surface Without penetration o r sporulation. Under these conditions, vitroplants of clones resistant by Vf and Vm genes expressed their resistance when inoculated with V. inaequalis race 1. The study of the overcoming of the Vm gene resista nce by race 5 of the pathogen showed aspects similar to those observed in the greenhouse. One of the applications of this study will be the rapid in vitro characterization of different races of the fungus.