櫻花流膠病藥劑防治之探討

Abstract

櫻花為薔薇科 (Rosaceae) 李屬 (Prunus) 樹木，具有超過 200 種以上之品種，為臺灣主要之行道樹和園藝景觀樹種。病蟲害、機械傷害、水分逆境皆可能造成櫻花枝幹上的流膠病徵，其中真菌性流膠病為常見病害，罹病處呈現潰瘍流膠、內部木材組織褐化，面臨逆境時可能導致病情加劇，造成枝條枯死甚至全株萎凋死亡。櫻花流膠病的病原菌種類尚未有詳細報導，目前認為與造成其他樹木流膠病或潰瘍病之菌種相同，為葡萄座腔菌科 (Botryosphaeriaceae) 之真菌。本研究針對臺北地區三處罹病櫻花及一處罹患潰瘍病的木棉進行病原菌分離，並以 internal transcribed spacer (ITS)、elongation factor 1-α 及 β-tubulin 序列進行親緣分析鑑定至種，共獲得兩株 Lasiodiplodia chiangraiensis (TP02、TY01)，及 Lasiodiplodia macroconidia (TP01)、Lasiodiplodia theobromae (TP03)、Botryosphaeria dothidea (TY02) 各一株。以菌絲塊創傷接種法建立穩定接種系統，將 5 菌株接種於山櫻花苗皆造成流膠病徵，且組織分離可重新獲得病原菌，完成柯霍氏法則。櫻花流膠病並無登記的藥劑防治方法，本研究選用 7 種作用機制之 9 種殺菌劑，於含藥培養基上檢測對 5 菌株菌絲生長之抑制能力，發現貝芬替、百克敏及得克利的抑制效果最佳。殺菌劑在木本植物上之系統移行性資訊向來較為缺乏，本研究使用實驗室已建立之茄苳 (Bischofia javanica) 苗根部浸泡及莖部注射法，檢測藥劑之向上及向下移行性，發現所有藥劑皆有向上移行能力，以滅達樂於根部浸泡法和得克利、普克利於莖部注射法中之向上移行效率最佳；百克敏、得克利和普克利則可檢測出低濃度向下移行。綜合藥劑之敏感性和移行性試驗結果，選用得克利為溫室防治試驗藥劑。將 L. theobromae TP03 和 B. dothidea TY02 接種於山櫻花樹苗上，並以預防性/治療性澆灌、預防性/治療性莖部注射、莖部塗抹等 5 種方式施藥，每週觀察罹病度並計算病害發展階梯下面積，6 週後進行組織分離。預防性注射能顯著降低病害發展階梯下面積和回分率，顯示具有抑制病原菌侵染拓殖的能力，防治效果最佳；莖部塗抹則能降低病害發展階梯下面積，顯示有助於減緩外部病徵，然而回分率結果說明未能抑制內部病原菌之拓殖。

Ornamental cherry trees (Prunus spp., Rosaceae), with more than 200 varieties, are major street and ornamental trees in Taiwan. Pests, mechanical injury, and water stress can cause gummosis on the stem and branches of cherry trees. Among these, fungal gummosis is a common disease, characterized by canker, gum oozing, and internal wood tissue browning. Under stressful environment, the disease will become more severe, causing branches or even the entire plant to wither and die. The pathogens of ornamental cherry gummosis disease are not yet fully investigated, but they are believed to be the fungi belonging to Botryosphaeriaceae family that cause gummosis and canker disease on trees. In this study, pathogens were collected from diseased ornamental cherry trees at three locations and from a cotton tree with canker disease at one location of Taipei. Isolates were identified to the species level by multi-locus phylogenetic analysis using internal transcribed spacer (ITS), elongation factor 1-α, and β-tubulin gene analysis. Two isolates of Lasiodiplodia chiangraiensis (TP02, TY01), as well as one each of Lasiodiplodia macroconidia (TP01), Lasiodiplodia theobromae (TP03), and Botryosphaeria dothidea (TY02), were obtained. A stable inoculation system, wounded inoculation with a mycelial disc, was established. Koch’s postulates were fulfilled for all five isolates: inoculation on Prunus campanulata Maxim seedlings caused gummosis disease symptoms, and the pathogen could be re-isolated from infected tissues. At present, there are no fungicides recommended for ornamental cherry gummosis disease. Nine fungicides with seven modes of action were selected to assess their efficacy in inhibiting the in vitro mycelial growth of the five isolates. The fungicide sensitivity tests showed that carbendazim, pyraclostrobin, and tebuconazole were the most effective. Information on the systemic activity and translocation of fungicides in woody plants has been limited. In this study, previously developed root-tip immersion and stem-injection methods on Bischofia javanica seedling were used to evaluate the acropetal and basipetal translocation ability of fungicides. Translocation tests indicated that all fungicides exhibited acropetal translocation, with metalaxyl by the root-tip immersion method and tebuconazole and propiconazole by the stem-injection method showing the highest acropetal translocation efficiency. Additionally, basipetal translocation of low concentrations of pyraclostrobin, tebuconazole, and propiconazole was detected. Based on the results of fungicide sensitivity and translocation assays, tebuconazole was selected for greenhouse control assay. L. theobromae TP03 and B. dothidea TY02 were inoculated on P. campanulata seedlings, and five treatment methods including preventive/curative drenching, preventive/curative stem injection, and stem painting were tested. Disease severity was rated every week and the area under the disease progress stairs (AUDPS) was calculated. Tissue isolation was conducted six weeks after inoculation. Preventive injection significantly reduced AUDPS and re-isolation rate, indicating its best control efficacy in inhibiting pathogen colonization. Stem painting helped reduce AUDPS, suggesting it alleviated external symptoms, but the re-isolation rate indicated that it did not effectively inhibit internal pathogen colonization.