Interactions of the nonhost French bean plant (Phaseolus vulgaris) with parasitic and saprophytic fungi. II. Fungal development after inoculation by injection or wounding

Abstract

Germination and growth of four saprophytic and five parasitic fungi nonpathogenic on French bean (Phaseolus vulgaris L. cv. Pinto) were examined in leaves after the epidermis was bypassed by injection or wounding. In unheated leaves, only the parasites had the ability to spread from the wound site and to germinate and grow inside the tissue after injection. The saprophytes behaved similarly only after the leaves were given a preinoculation heat treatment, suggesting a sensitivity to heat-sensitive inhibitors. For two of the saprophytes, evidence for the presence of heat-insensitive inhibitors also was found. Unlike the intercellular growth following stomatal penetration, growth of all of the parasites was affected by heat-sensitive defenses once the epidermis was bypassed. The greater intercellular growth after injection as compared with stomatal penetration suggested that the guard cells play a significant role in the resistance of intact, unheated leaves to Cladosporium fulvum Cooke. Of the saprophytes examined, Neurospora crassa Shear & Dodge appeared to posses a number of attributes that might be considered as potential pathogenicity factors.