(67(4):387-400)Physiological Characteristics, Pathogenicity and Fungicide Screening of Citrus Alternaria Brown Spot Disease Caused by Alternaria alternata

柑橘褐斑病在2012–2013 年間於台灣之「茂谷柑」、「佛利蒙柑」及「帝王柑」等柑橘園區之春梢期陸續發生。本研究除針對該病原菌進行生理特性調查外，亦對不同柑橘品種之病原性及其防治藥劑進行篩選評估。柑橘褐斑病菌分離株 (Alternaria alternata Alt-001) 可在「茂谷柑」、「明尼橘柚」、「桶柑」、「佛利蒙柑」、「晚崙西亞」、「豔陽柑」及「台農天王柑」等柑橘品種之離葉嫩葉傷口接種時，造成褐色病斑，但在粗皮檸檬之嫩葉上則不造成病斑。本病原最適菌絲生長溫度為25℃，而25–30℃為孢子發芽最適溫度。測試殺菌劑對其菌絲生長及孢子發芽影響時，結果顯示快得寧在10 mg a.i. L-1 有效濃度下可有效抑制菌絲生長，抑制率達99.2%；而快得寧、氫氧化銅、鋅錳乃浦及扶吉胺等4 種藥劑可顯著降低病原菌之孢子發芽，其中植株噴布快得寧、氫氧化銅及鋅錳乃浦藥劑處理21 d 後，A. alternata Alt-001分離株在其葉片上之孢子發芽率仍顯著低於噴布水之對照組。快得寧、氫氧化銅、鋅錳乃浦及扶吉胺為目前官方推薦柑橘真菌性病害之防治藥劑，從藥效評估結果，上述藥劑可一併作為防治柑橘褐斑病之用藥。 Alternaria brown spot of citrus (Citrus reticulata) was found in orchards of ‘Murcott’, ‘Fremont’, and ‘Gonggan’ citrus in Taiwan during 2012–2013. This disease seriously affected the growth of citrus in spring shoot period. The objective of this study is to investigate the physiological characteristics and pathogenicity of Alternaria alternata, the causal agent of the brown spot disease, and further screen the effectiveness of fungicides. Seven cultivars included ‘Murcott’, ‘Minneola’, ‘Tankan’, ‘Fremont’, ‘Valencia’, ‘Sunburst’, and ‘Tainung Giant’. Results showed that brown-to-black lesions appeared on the detached young leaves inoculated through wounds, but no symptom appeared on rough lemon after wound inoculation. The optimal temperature for mycelial growth and spore germination of A. alternata strain Alt-001 and Alt-008 was 25℃ and 25–30℃, respectively. Mycelial growth was effectively inhibited by 10 mg a.i. L-1 oxine-copper, the inhibition rate of 99.2% was measured by screening. Spore germination of A. alternata was inhibited by oxine-copper, copper(II) hydroxide, mancozeb, and fluazinam in vitro. Futhermore, spore germination of A. alternata was continuously inhibited by oxine-copper, copper(II) hydroxide, and mancozeb in greenhouse 21 d after fungicide treatment. These fungicides have been recommended to control other fungal diseases of citrus. Therefore, it is suggested that they could also be used to control Alternaria brown spot of citrus in term of efficacy