臺灣木瓜炭疽病菌之鑑定

Identification of Colletotrichum species associated with papaya anthracnose in Taiwan

由Colletotrichum spp.所引起的木瓜炭疽病是木瓜主要病害之一，受害果實腐壞，喪失商品價值。本研究選取2014~2022年分離自臺灣各地木瓜果實的28株炭疽病菌，以分生孢子形態及多基因親緣關係分析進行菌種鑑定並測其病原性。依據分生孢子形態及ITS序列，供試菌株分屬以下5個複合種（species complex, SC）：C. acutatum species complex（CASC）、C.gloeosporioides species complex（CGSC）、C. magnum speciescomplex（CMSC）、C. orchidearum species complex（COSC）及C. truncatum species complex（CTSC）。鏈結多基因（ACT、CHS-1、GAPDH及TUB2）及ITS核酸序列作親緣關係分析得知，木瓜炭疽病菌菌種依其菌株數分別為C. okinawense（CMSC，10株）、C. tropicale（CGSC，6株）、C. fructicola（CGSC，4株）、C. siamense（CGSC，2株）、C. plurivorum（COSC，2株）、C.truncatum（CTSC，2株）、C. schimae（CASC，1株）及1株屬CGSC之待鑑定種。以上8種炭疽病菌均可於台農2號木瓜果實以人工接種產生中央褐色周圍水浸狀，其上著生鮭魚色分生孢子堆之炭疽病徵。除卻C. okinawense及C. plurivorum，其他5個菌種均為台灣地區首次報導之木瓜炭疽病菌。

Papaya anthracnose caused by Colletotrichum spp. affects fruit quality and market values considerably. Twenty-eight isolates collected from papaya fruit during 2014~2022 in Taiwan were used for species identification and pathogenicity tests in this study. Based on conidial morphology and ITS sequences, the isolates were classified into 5 species complexes: C. acutatum species complex (CASC), C. gloeosporioides species complex (CGSC), C. magnum species complex (CMSC), C. orchidearum species complex (COSC) and C. truncatum species complex (CTSC). Phylogenetic analyses of the isolates were performed by using ITS and 4-gene dataset (ACT, CHS-1, GAPDH and TUB2). These analyses confirmed that C. okinawense (10 isolates) was the dominant species followed by C. tropicale (6 isolates), and C. fruticola (4 isolates). Moreover, there were 2 isolates for each species of C. plurivorum, C. siamense, and C. truncatum, and 1 isolate for C. schimae. Additionally, we also found one unidentified isolate belongs to CGSC. Inoculation of a representative isolate of each species could cause anthracnose symptoms on mature papaya fruit (cv. Tainung No.2), and the same fungus was re-isolated from symptomatic fruit, thus fulfilling Koch's postulates. Except for C. okinawense and C. plurivorum, the other 5 species were reported to be the pathogens of papaya anthracnose for the first time in Taiwan.