Resistance of narcissus to infection by Fusarium oxysporum f.sp. narcissi

Abstract

Single hyphae of Fusarium oxysporum f.sp. narcissi were capable of direct penetration of intact, unwounded, root tips of the susceptible narcissus cv. Golden Harvest. In other parts of the root, penetration involved the formation of infection cushions. In general, advance of the fungus in roots was by inter- and intracellular growth. In bulb scales spread occurred via ducts prior to invasion of surrounding tissue. In roots of the resistant cv. St Keverne, epidermal cell walls were modified in the presence of the fungus and lignituber-like structures were deposited about invading hyphae. Such structures were not produced in root cap cells. Isolated bulb scales expressed differential resistance to F. oxysporum f.sp. narcissi, indicating that a significant part of the resistance of cv. St Keverne has a physiological basis. The accumulation of antifungal compounds, including 7-hydroxyflavan and 7,4′-dyhydroxy-8-methyflavan, was compared in bulb scales of Golden Harvest and St Keverne following wounding or inoculation with the pathogen. It was concluded that resistance involves a complex interaction between the accumulation of antifungal compounds following infection, cell wall modification, and the formation of lignituber-like structures.