Pathogenesis ofVenturia inaequalison Shoot-Tip Cultures and on Greenhouse-Grown Apple Cultivars

Four apple (Malus × domestica) cultivars with different levels of resistance to Venturia inaequalis, the incitant of apple scab, were grown in the greenhouse and as shoot-tip cultures in vitro. Young, actively growing leaves were inoculated with a conidial suspension. Development of the fungus during the early events of pathogenesis and concurrent host responses were observed by light and electron microscopy. Prepenetration and penetration activities were indistinguishable in resistant and susceptible cultivars grown in vitro or in the greenhouse. After penetration, however, colonization and establishment of the fungus differed among cultivars and growing conditions [...]