Journal of Taiwan Agricultural Research

Author:Chiao-Wen Huang, Chao-Jung Wu, Hong-Ren Yang, Su-Yu Lai, and Hui-Fang Ni*

Abstract:

    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.

Key words:Citrus (Citrus reticulata), Alternaria brown spot, Alternaria alternata, Fungicides screening

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