PENETRATION OF CUCUMBER LEAVES BY COLLETOTRICHUM-LAGENARIUM IS REDUCED IN PLANTS SYSTEMICALLY PROTECTED BY PREVIOUS INFECTION WITH THE PATHOGEN

Microscopic examination of whole mounts and sectioned leaf tissue indicated that penetration of cucumber leaves by Colletotrichum lagenarium was reduced in both resistant and susceptible cultivars when the plant was systematically protected by previous infection with the pathogen. Differences were not observed, however, in the number of appressoria produced on protected or unprotected leaves. The degree of protection was reduced by puncturing or abrading the leaf surface of the susceptible cultivars prior to inoculation, and protection was lost by removing a portion of the leaf's epidermal tissue and inoculating the exposed sites with the fungus. Protection was not effective at leaf sites with the epidermis removed even when low concentrations of inoculum were used. Removal of epidermis did not reduce resistance or protection of a resistant cultivar. The resistance of the cultivars Calypso, Addis and Liberty to anthracnose was not due to a reduction in the formation of appressoria or penetration, but was associated with rapid necrotization of penetrated cells. Infectious C. lagenarium was isolated from lesion-free inoculated areas on leaves of systematically-protected plants up to one week after inoculation. © 1979.