台灣瓜類疫病之調查、病原菌鑑定及病原性測定

Abstract

自1980至2015年調查台灣瓜類疫病之發生情形，其中62區罹病田的瓜類罹病組織上可以分離出疫病菌，分離得到的疫病菌經形態特性鑑定與核醣體內轉錄區間 (ITS) DNA基因序列比對，危害我國的瓜類疫病菌主要有兩種，包括 Phytophthora melonis (甜瓜疫病菌) 與 Phytophthora capsici (番椒疫病菌)。其中P. melonis分離自36處瓜園，共獲得100菌株，其中44株為A^1菌株，56株為A^2菌株，寄主包括胡瓜、冬瓜、扁蒲、甜瓜(包括洋香瓜、甜瓜、美濃瓜) 及西瓜，該菌主要危害胡瓜的莖基部、果實及幼苗，與其他瓜類的果實。而P. capsici則自26處瓜園分離得到，共77菌株，其中27株為A^1菌株、50株為A^2菌株，寄主包括胡瓜、冬瓜、南瓜、玩具南瓜、扁蒲、甜瓜及西瓜，該菌主要侵染寄主的果實，亦可造成幼苗猝倒與莖基部腐敗。此外，分離到的疫病菌接種於原先分離的寄主時，均會產生與田間相同的病徵，再分離亦可得到相同病原菌。另比較P. melonis和P. capsici對於不同瓜類作物的侵染力，結果顯示兩種疫病菌對胡瓜、冬瓜、南瓜、扁蒲、香瓜、西瓜的幼苗均有相當的致病力，但絲瓜與苦瓜則否。此外，自瓜類分離的P. capsici菌株可以感染甜椒‘藍星’，但P. melonis則否。而疫病菌危害冬瓜、南瓜、扁蒲在台灣為首度報導。 A survey of Phytophthora diseases of cucurbit crops in Taiwan was conducted from 1980 to 2015 and Phytophthora species were detected in 62 cucurbit fields. Analysis of morphological characteristics and RNA Internal Transcription DNA Sequence (ITS1-5.8S rDNA-ITS2) of these isolates revealed that Phytophthora melonis and Phytophthora capsici were two predominant species found in Taiwan cucurbit fields. Analysis of 100 P. melonis isolates obtained from 36 sites revealed that 44 isolates were A^1 and the remaining isolates were A^2. P. melonis was primarily isolated from diseased cucumber (Cucumis sativus), wax gourd (Benincasa hispida), bottle gourd (Lagenaria siceraria), melon (Cucumis melo), and watermelon (Citrullus vulgaris). Analysis of P. capsici 77 isolates collected from 26 fields revealed that 27 isolates were A^1 and 50 isolates were A^2. P. capsici was isolated from cucumber, wax gourd, Chinese squash (Cucurbita moschata), ornamental gourd (Cucurbita pepo var. ovifera), bottle gourd, melon and watermelon. Phytophthora melonis mainly attacked the basal stems, fruits and young seedlings of cucumber and the fruits of other cucurbit plants in the fields. In contrast, P. capsici mainly induced fruit rot of the infected plants, but sometimes it also caused seedling damping-off and basal stem rot. All Phytophthora isolates collected from cucurbit belonged to the typical types of P. melonis or P. capsici. Pathogenicity assays revealed that the pathogens caused symptoms resemble those found in the fields and the same pathogen could be reisolated from all artificially infected tissues. Pathogenicity tests showed that both Phytophthora species were highly virulent to the seedlings of cucumber, wax gourd, Chinese squash, bottle gourd, melon and watermelon, but not to bitter melon (Momordica charantia) and luffa (Luffa cylindrica). In addition, P. capsici but not P. melonis isolated from cucurbit plants was highly virulent to sweet pepper. To our knowledge, this is the first report of Phytophthora spp. causing diseases on wax gourd, Chinese squash and bottle gourd in Taiwan.