| Summary: | 碩士 === 國立中興大學 === 植物病理學系所 === 106 === Cucurbitaceae is an important crop distributed over the world widely. In Taiwan, loofah, bitter gourd and cucumber are three vegetables common in the field. However, several infectious fungal diseases are severe during growth season. Among the diseases, the Fusarium wilt caused by Fusarium oxysproum (Fo) is one of the most important diseases in cucubit production area. Currently, more than 150 formae speciales have been recorded throughout the world. Although formae speciales show the pathogenic specificity on original host, the cross-pathogenicity has been found generally within cucurbitaceae Fusarium wilt. Besides, there are several factors affecting the cross-pathogenicity such as cultivar, temperatuer, plant stage, and method of inoculation. Therefore, combining pathogenicity tests with molecular phlogeny analysis would help the identification of formae speciales. In Taiwan, grafted bitter gourd (with loofah stock) is widely used to prevent Fusarium wilt in the filed, however, grafted bitter gourd still wilt in recent years. It is necessary to clarify if F. oxysproum f. sp. momordicae (Fomo) is cross pathogenic to loofah stock or F. oxysproum f. sp. luffae (Folu) already arrive at the soil. In this study, the F. oxysproum obtained from cucumber, bitter gourd, and loofah were used to examine the pathogenicty and cross-pathogenicty with three cucurbits and phylogeny analysis was carried out . The results indicated that F. oxysproum isolates from cucumber and bitter gourd could infect loofah (open pollination, OP) and F. oxysporum isolates from loofah could infect cucumber (cv. Vantage) at 20°C based on root dipping method. In addition, some of loofah (cv. Merit) individuals could be infested by F. oxysporum isolates from bitter gourd at 28°C with root dipping method, but one isolate from loofah (Fomhl6) did not cause symptom on loofah under the same condition. Fomhl6 isolate colonized in loofah only. When we inoculated young stage plant (seedling with 2 cotyledons) by root dipping method, the symptom of cross-infection was even more severe. But when we inoculated plants with infested soil, cross-pathogenicity was not obvious. Also, we did the inoculation of grafted (loofah as stock, bitter gourd as scion) plants to mimic the plant infested in the field. The results revealed the main influence isolates on grafted plant was Folu. For the distribution of isolates in grafted plant, we found that Folu could be distributed in the whole plant, however, Fomo was limited in hypocotyl (or stock). Finally, results of phylogeny analysis indicated the F. oxysporum isolates from three cucurbits did not associate with host specificity based on rDNA intergenic spacer (IGS) and translation elongation factor-1α (EF-1α) sequences. However, the sequences of secreted in xylem 6 (SIX6) gene, which associated with pathogenicty, could separate the F. oxysporum isolates from three cucurbits.
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