- 期刊
由Corynespora cassiicola引起之羅勒枝枯病
Corynespora cassiicola Causes Dieback on Basil
摘要
羅勒枝枯病（basil dieback）為羅勒栽培時期的真菌病害之一，於屏東縣萬丹鄉發現羅勒植株的枝條於採收後，從枝條傷口處開始乾枯，呈現黑褐色壞疽狀病徵，逐漸蔓延至全株、死亡。從不同羅勒栽培區，相同病徵的罹病組織中分離出同一種真菌。室溫下，於馬鈴薯葡萄糖瓊脂（potato dextrose agar; PDA）培養10 d後，呈現邊緣為白色至淺灰色，中央為深橄欖綠色的菌落。根據此病原菌之型態特徵，與核醣體核酸基因（rDNA）的內轉錄區（internal transcribed spacer; ITS）序列鑑定結果，將該病原菌鑑定為Corynespora cassiicola，並以柯霍氏法則證明，此真菌為造成羅勒枝枯病之病原菌。菌絲生長溫度範圍為15－35℃，孢子發芽溫度範圍為10－35℃。在25℃下，維持連續48 h高濕度環境中，羅勒枝枯病之罹病率可達75%，為此病害最適發病條件。評估植物保護資訊系統中，羅勒葉斑病（Alternaria alternata引起）之推薦用藥，四氯異苯腈、保粒黴素（甲）、依普同與克收欣，於濃度1、10與100 ppm，對羅勒枝枯病菌菌株CC-2、CC-3在PDA上菌絲生長之影響。結果發現，依普同對CC-2與CC-3均有最佳的菌絲生長抑制率，分別為64.4－77.0%與65.0－75.4%；克收欣次之，分別為60.7－66.8%與58.8－63.6%，而四氯異苯腈與保粒黴素（甲）則介於40－50%。故依羅勒葉斑病（A. alternata, leaf spot）推薦藥劑之稀釋倍數使用，可同時防治羅勒枝枯病發生。
並列摘要
Basil (Ocimum basilicum L.) is a perennial herb belonging to the family lamiaceae, and is commonly cultivated as a condiment or spice in Taiwan. A symptom of dieback appeared on basil planted in the field and greenhouse at Wandan Township, Pingtung Country, and Luzhu Township, Kaohsiung City, Taiwan, during September 2019 to March 2020. The dark brown lesion initiated from the cutting ends made by the regular harvest, then extended progressively, and eventually resulted in the dieback of the branches and defoliation. Conidiophores and conidia characteristics of Corynespora cassiicola were observed from diseased tissues. Margin of lesion was excised and sterilized. Hyphae, once emerged from the plant tissue, were transferred from water agar, subcultured on potato dextrose agar (PDA) plates, and incubated at room temperature. The colonies on PDA were white to pale gray in color and dark olive green in the center area. After 25 days incubation, conidia characteristics of C. cassiicola were observed at middle of the colony. Genomic DNA was extracted from pure cultures. The internal transcribed spacer (ITS) DNA fragment was amplified by PCR with primer pairs: CoryITS-f1 and CoryITS-r1, and sequenced. ITS sequence was blasted with GenBank on National Center for Biotechnology Information (NCBI). Blast analysis showed that CC-2 and CC-3 had 100% identity to C. cassiicola. Necrosis or dieback appeared at seventh day on some inoculated basils, with disease severity being 75% at 25℃, while 16.67% at 20℃ and 30℃. C. cassiicola was reisolated from the lesions, thus fulfilling Koch's postulate. The results suggested that the optimal condition for C. cassiicola to cause dieback of basil was at 25℃ in high humidity. Fungicides, which recommended on control of leaf spot caused by Alternaria alternata were tested and revealed that iprodione effectively inhibited mycelial growth of C. cassiicola.