Immunolocalization of a class III chitinase in two muskmelon cultivars reacting differently to Fusarium oxysporum f. sp. melonis.

Fusarium oxysporum f. sp. melonis is a highly specialized fungus that attacks the root system of melon (Cucumis melo L.). In this work the presence of a class III chitinase was examined by immunological techniques in the root and stem base of a susceptible (cv. Galia) and a resistant (cv. Bredor) melon during the infection process. By immunolocalization it was not possible to detect the constitutive presence of class III chitinase in any of the cultivars. However, the immunolabelling appeared in the root tissues of both cultivars as a consequence of wounding and of infection by F. oxysporum f. sp. melonis. Distinct patterns of chitinase detection were observed in the roots of the two cultivars as the infection progressed. Furthermore, by western blotting distinct class III chitinase isoforms were detected, which responded differently to the F. oxysporum f. sp. melonis infection. Our results strongly indicate that a relationship exists between class III chitinase and melon resistance to Fusarium infection, and that the resistance is associated with certain isoforms of this enzyme.