柑桔潰瘍病之非農藥防治

Abstract

柑桔潰瘍病（Citrus Bacterial Canker）是目前國際柑桔栽培上最重要且最具破壞性的一種細菌性病害，病原菌為Xanthomonas axonopodis pv. citri。在臺灣，潰瘍病最早記載於1932年，1952年已成為柑桔產業的主要病害。潰瘍病可發生於柑桔的葉片、果實、枝條上，病斑中央部份呈灰白色凹陷，周圍呈現褐色木栓化之結構，表皮破裂而粗糙堅硬，在葉片上的病斑邊緣常有黃色暈圈，嚴重罹病之葉片逐漸黃化後落葉。Vauterin等人於1995年將柑桔潰瘍病菌重新分類如下：X. axonopodis pv. citri（原X. campestris pv. citri A病原型）；X. axonopodis pv. aurantifolii（原X. campestris pv. citri B、C、D病原型）；X. axonopodis pv. citrumelo（原X. campestris pv. citri E病原型）；而本研究之田間調查發現，臺灣柑桔潰瘍病菌中，有90%屬於A病原型。柑桔潰瘍病之藥劑防治主要為施用銅劑，如4-4式波爾多液、56%氧化亞銅可濕性粉劑、81.3%嘉賜銅可濕性粉劑等；但銅劑在高溫條件下易發生藥害，大量使用亦增加果園蟎類的危害並造成環境污染，甚至已有抗銅性的潰瘍病菌株出現。本試驗的目的在於，施用數種非農藥防治資材，包括重碳酸鹽、水楊酸、咖啡因、枯草桿菌、鏈黴菌發酵物、窄域油、大蒜萃取物等，利用殺菌、誘導抗病性、生物防治、物理防護等作用機制，進行柑桔潰瘍病之防治試驗，以開發出替代傳統藥劑之方法。在盆苗防治試驗之結果，顯示咖啡因與大蒜萃取物對柳橙潰瘍病、鏈黴菌發酵物與水楊酸對椪柑潰瘍病、水楊酸與鏈黴菌發酵物對白柚潰瘍病具有防治效果。在田間防治試驗之結果，顯示水楊酸與鏈黴菌發酵物對柳橙潰瘍病、鏈黴菌發酵物與大蒜萃取物對文旦潰瘍病與檸檬潰瘍病具有防治效果。另外值得注意的是，窄域油不論在盆苗防治試驗或田間防治試驗中，皆使柑桔潰瘍病的病勢加重。

Citrus bacterial canker (CBC), caused by Xanthomonas axonopodis pv. citri (Xac), is the most important and destructive disease in the international citrus industry. In Taiwan, the earliest report of citrus bacterial canker is in 1932, and it became the most important disease in local citrus industry in 1952. CBC occurs on the leaves, stems, and fruit. The lesions on leaves become raised and corky, surrounded by a chlorotic halo, and the centers of the lesions become gray and crater-like. Defoliation and twig dieback become a problem as the disease progresses on a plant. In 1995, Vauterin et al. reclassifies pathovars of Xanthomonas campestris as X. axonopodis pv. citri (original X. campestris pv. citri pathotype A), X. axonopodis pv. aurantifolii (original X. campestris pv. citri pathotype B, C, and D), and X. axonopodis pv. citrumelo (original X. campestris pv. citri pathotype E). Our field survey in Taiwan showed that 90% of Xanthomonas campestris are X. axonopodis pv. citri. Spraying with copper pesticides is a traditional disease control method against CBC, such as 4-4 Bordeaux mixtures, 56% cuprous oxide WP, and 81.3% Kasuran WP. However, copper pesticides can induce phytotoxicity at higher temperature, increase mite population in citrus orchard and cause environmental pollution if over-used. It may produce the anti-copper strains of Xac. For these reasons, the purpose of this study is to develop non-pesticide control methods for CBC by using bicarbonates, salicylic acid, caffeine, Bacillus subtilis, fermentation products of Streptomyces candidus, narrow-range oil, and garlic extract. The action mechanisms for these non-pesticide material are killing, systemic acquired resistance, biological control, and physical protection. Results of pot experiments in the greenhouse showed that caffeine and garlic extract were effective in suppressing CBC on orange, fermentation products of Streptomyces candidus and salicylic acid on ponkan, and salicylic acid and fermentation products of Streptomyces candidus on Madou peiyu. Results of field experiments, conducted on NTU farm, showed that salicylic acid and fermentation products of Streptomyces candidus were effective in suppressing CBC on orange, fermentation products of Streptomyces candidus and garlic extract on Madou pomelo and lemon. It is worth to note that narrow-range oil increased CBC in both pot and field experiments.