櫻花立枯萎凋及其管理之研究

Abstract

山櫻花 (Prunus companulata Maxim) 為落葉喬木，一到春天便會開滿緋紅色花朵，廣受國人喜愛。但在新闢或更新之公園綠地，經常性發生山櫻花植株立枯或半邊立枯之情形，發生比例可達三成甚至五成，死亡之山櫻花需進行移除與補植，在養護上造成極大困擾。因此本研究目的即為探討山櫻花立枯發生之原因，並針對其原因發展防治之對策，希望可以解決山櫻花立枯之問題。經由臺大校園、臺北市、新北市、臺中市等地區之田間山櫻花立枯調查，發現立枯多發生於新植或移植地區，而當地立地環境不良如排水不良與覆土過深也與之相關，故在上述環境中容易發生山櫻花立枯。在訪問園藝業者時，業者多表示山櫻花本身沒有致命病蟲害，在移植中對環境要求甚高，容易枯死。在颱風過境觀察倒伏之山櫻花根部發現，其根部在移植後新根生長量少，斷根也沒有癒合。又依據林業試驗所 2014年林木疫情通報共 2036例中，山櫻花僅 29 例，含 3 例褐根病，以逆境、移植不當、淹水為主要害因。再依重要 14 種非傳染性害因加以分析，歸納危害山櫻花的主要害因應為立地環境異常、耕作或移植不當、缺氧或浸水、缺水等項目。本研究對立枯之山櫻花根部進行病原菌分離，目前並沒有發現造成山櫻花病害常見之病原菌。在淹水不缺氧之裸根浸水試驗中，山櫻花植株可維持一個月不會死亡。在淹水加葡萄糖-麩胺酸造成缺氧之裸根與盆栽試驗中，山櫻花植株 3 天即有萎凋症狀，10 天即可造成植株死亡。以有機肥加淹水造成缺氧者，約 3 天造成萎凋，達 9 天可致死。在缺水乾旱復甦試驗中，山櫻花植株出現萎凋症狀後澆水復甦，萎凋初期葉片下垂之狀態可以完全回復，萎凋末期葉片脆化者，死亡率超過一半。在高溫不缺水試驗中，山櫻花植株可以忍受白天氣溫 40℃ 連續 20 天不發生萎凋。綜合以上結果，山櫻花的立枯或半立枯，並非病原生物所造成，而是由不良環境加上本身傷口不易癒合，不易長新根所造成。其防治也應以小苗移植、避免移植傷根、增大根球、加強養根、選擇良好基地等為原則。

Taiwan cherry (Prunus companulata Maxim) is a native deciduous tree species in Taiwan. In spring season, it usually bloom plentifully and brightly, making is a favorite flowering plant of Taiwan people. However, when people plant the Taiwan cherry in new park or transplant them, there was a great opportunity that they suffered from the wilting, decline and even death situation. The ratio of decline or half decline may as high as 30 to 50%, making the maintenance a big burden to the horticulturalist as the dead tree need to be removed and replaced frequently. Thus, this study is aimed to investigate the reason of Taiwan cherry wilting or decline, and to develop the strategy of control it. By surveying the Taiwan cherry decline in NTU, Taipei, New Taipei and Taichung, it was found decline usually occurred in newly planted or transplanting area, and the problem usually correlated with poor planting site such as poor drainage and thick covering soil. In the interview with local horticulturalist, they responded that the Taiwan cherry doesn’t have lethal diseases or pests, but it require a higher standard of environmental factor in transplantation. After typhoon striking in 2015, we investigated the wind-fell trees. We found that the roots of Taiwan cherry did not grow new rootlets after transplanting, and the cutting wound did not recover at all. According to the Taiwan Forest Epidemic Reporting System in 2014 that collected by Taiwan Forest Research Institute, among the 2036 cases of reported pests or disorders in Taiwan, only 29 cases were belong to Taiwan cherry or other cherry. This list contained 3 cases of root rot disease, while 42% or 12 cases were related with environmental stress, improper transplanting or flooding situation. Based on factor analysis by our lab, among 14 important non-infectious factors, major harmful factors of Taiwan cherry decline were poor planting site, improper cultivation or transplanting, oxygen deficit or flooding, and drought. In this study, we isolated the fungi and bacteria pathogen from the root of wilted Taiwan cherry, but did not find the common pathogens that cause diseases on Taiwan cherry at present. In the flooding test of bare root without oxygen deficit, Taiwan cherry can keep healthy for one month without death. In the flooding test of Taiwan cherry with bare root added with glucose-glutamine solution to make the oxygen deficit, they showed wilting symptom in about 3 days, and caused plant death in about 9 days. In the flooding test of pot plant with organic fertilizer added into soil, Taiwan cherry showed wilting symptom in about 3 days, and caused plant death in about 9 days. In the test of recovery after drought, Taiwan cherry can recover very well when in early stage or drought index 1. In this early drought stage the drooping leaves can completely recover after watering, but in the late stage the brittle leaves may not recover with mortality rate over 50%. In the test of high temperature without drought, Taiwan cherry can stand for day temperature at 40℃ continued for 20 days without wilting. Based on the above results, the Taiwan cherry decline or half decline is not caused by biotic pathogens, but caused by poor environment, difficult wound healing and difficult to grow new root. The prevention of wilting or decline, therefore should pay attentions to transplanting in young stage, avoiding the root wounds, enlarging the root core, improving the root culturing, and choosing a better environment.