Study on decline of Taiwan Cherry and its management

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.