| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 87 === This study was aimed at determining the cause and some basic information of Fusarium wilt of cucumber and screening the nonpathogenic Fusarium oxysporum for its biological control. This disease did not occur in every cucumber field, but in some fields, their disease incidence had up to 25%-75% during the 1997-1998 survey. The disease cucumber was commonly in patches and showed not only damping-off of seedlings, vascular discoloration and wilt of adult plants, but characteristically showed rot symptoms on peg, primary root and several secondary roots. Based on completion of Kock’s Postulates, and cross-inoculation tests on seedlings of cucumber and other cucubitaceous plants indicated that the Fusarium from cucumber was pathogenic on cucumber, melon, muskmelon, and oriental pickling melon, but not on watermelon, bitter gourd and loofah. Moreover, The wilt fusaria from muskmelon, watermelon, bitter gourd, and loofah were pathogenic on their original hosts, but not on cucumber. Therefore, the Fusarium from cucumber was identified as F. oxysporum f. sp. cucumerinum Owen. The isolation frequence of the pathogen from cucumber seeds (Vantage) obtained from market was 0.4%. The pathogen could penetrate cucumber plants from peg and secondary roots and causeing damping-off and wilt symptoms, respectively. In the cross-protection tests, among 173 isolates of nonpathogenic F. oxysporum, an isolate (Fo-366) obtained from Hualian soil could protect cucumber plants from F. oxysporum f. sp. cucumerinum for at least 42 days after challenge inoculation. Hualian soil was proved to be a suppressive soil to Fusarium wilt of cucumber by soil infestation inoculation method in greenhouse. The possible suppressive factors in Haulian soil were discussed. Colonies of isolates Fo-366 (nonpathogenic F. oxysporum) and Foc-100 (pathogen) produced different pigmentation and could be distingushed from each other easily when grown on a modified PCNB medium (using 2% galactose instead of 1.5% peptone).
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