Chen Chong, Li Bao-Hua, Dong Xiang-Li, Wang Cai-Xia, Lian Sen, Liang Wen-Xing
College of Crop Protection and Agronomy, Qingdao Agricultural University, Key Lab of Integrated Crop Pests Management of Shandong Province, Qingdao, Shandong 266109, P. R. China.
Plant Dis. 2016 Dec;100(12):2394-2401. doi: 10.1094/PDIS-05-16-0625-RE. Epub 2016 Sep 15.
Valsa canker, caused by Valsa mali, is a destructive disease of apple in China. The pathogen infects apple branches, mainly through pruning wounds, and causes branch and tree death. To determine the conditions required for V. mali infection through pruning wounds and growth within the xylem, pruning wounds on 1- to 4-year-old apple branches were inoculated with conidia in vitro under artificially controlled conditions and in vivo in the orchard. The effects of temperature, wetness duration, and wound age on conidial infection through pruning wounds as well as hyphal growth in the xylem were examined. The results showed that, after invading through pruning wounds, V. mali hyphae grew along xylem vessels, tracheids, and rays, expanding longitudinally and laterally. The hyphae could enter adjacent xylem vessels and tracheids through micropores to form a dense hyphal network. Wetness duration did not exhibit an essential effect on conidial infection from pruning wounds. Conidia spread to pruning wounds with rainwater could infect the xylem without any other extra moisture. Temperature for V. mali conidia infection through pruning wounds and hyphal extension in the xylem ranged from 5 to 35°C, with the optimum at 20°C. Pruning wounds made in late March were susceptible to V. mali infection in March, April, and May; the susceptibility was markedly deceased by June, and the pathogen could barely infect through the pruning wounds in November. The infected pruning wounds began to show symptoms from the spring of the following year. More than half of the observed Valsa canker lesions emerged in the spring of the second year, and new canker twigs were also developed from the inoculations in the spring of the third year. March, April, and May are the critical periods for protecting pruning wounds against infection by V. mali in China, and coating pruning wounds with protective film immediately after pruning is an easy and effective measure to protect the pruning wounds.
苹果腐烂病由苹果黑腐皮壳菌引起，是中国苹果的一种毁灭性病害。病原菌主要通过修剪伤口侵染苹果枝条，导致枝条和树木死亡。为了确定苹果黑腐皮壳菌通过修剪伤口侵染以及在木质部内生长所需的条件，在人工控制条件下于体外以及在果园内于体内，用分生孢子接种1至4年生苹果枝条上的修剪伤口。研究了温度、湿润持续时间和伤口龄期对分生孢子通过修剪伤口侵染以及在木质部内菌丝生长的影响。结果表明，苹果黑腐皮壳菌的菌丝通过修剪伤口侵入后，沿着木质部导管、管胞和射线生长，纵向和横向扩展。菌丝可通过微孔进入相邻的木质部导管和管胞，形成致密的菌丝网络。湿润持续时间对分生孢子从修剪伤口的侵染没有本质影响。随雨水传播到修剪伤口的分生孢子无需任何额外水分即可侵染木质部。苹果黑腐皮壳菌分生孢子通过修剪伤口侵染以及在木质部内菌丝延伸的温度范围为5至35℃，最适温度为20℃。3月下旬造成的修剪伤口在3月、4月和5月易受苹果黑腐皮壳菌侵染；到6月敏感性明显降低，11月病原菌几乎不能通过修剪伤口侵染。受侵染的修剪伤口从次年春季开始出现症状。观察到的苹果腐烂病病斑一半以上在第二年春季出现，第三年春季接种处也长出新的病枝。在中国，3月、4月和5月是保护修剪伤口免受苹果黑腐皮壳菌侵染的关键时期，修剪后立即用保护膜覆盖修剪伤口是保护修剪伤口的一种简便有效的措施。
