Protection of Cucumber Against Anthracnose by a Hypovirulent Strain of Fusarium oxysporum f. sp. cucumerinum

Abstract

Cross-protection of the cucumber anthracnose by a hypovirulent strain of Fusarium oxysporum f. sp. cucumerinum was examined for seedlings of cucumber cvs. Suyo and Shogoin-Fushinari. Number and size of anthracnose lesion on first true leaf were reduced in both cultivars by the introduction of microconidia from hypocotyl cut-ends 2 to 4 weeks before the challenge inoculation with Colletotrichum lagenarium. Dipping of the cut-ends for 2hr into microconidia suspension at 2×10⁴ spores/ml was sufficient to reduce the anthracnose lesions. The inducer fungus survived mainly in hypocotyl and root, and no fungus was detected in the challenge site. This indicates that the induction of systemic resistance occurs at “hypocotyl and root to leaf” level. It was suggested by the experiments with culture filtrate and cell free fractions of budding spores that the systemic resistance is induced without agents which cause damage characteristic of Fusarium wilt, such as wilting and browning of vascular system. Cell wall fraction which was removed water soluble materials by autoclave was most effective to induce the systemic resistance.