苹果树腐烂病流行因子及其影响机制

Penetrating phellem layer and growing in xylem are two key processes controlling epidemics of apple scab, caused by Vlasa mali. The affection of all the factors on the epidemics the disease achieved by affecting the two key processes. This is different with other fungi diseases, for which the pathogen infection is the key processes restricting disease epidemics. Focusing on the two key epidemic processes, the present research project will: I. Investigate effects of three epidemic factors, i.e. low temptation, including freeze injury, vigors of apple tree and branch dehydration due to drought, on the epidemics of apple scab. Develop models to describe the relation-ship between the factors and disease epidemics. Understand, with the help of observation of tissue section, the mechanisms that the hypha penetrated phellem layer and how epidemic factors affect the penetration. Learn, with the help of molecular biological techniques, the genes and enzymes involved in penetrating processes. II. Examine the growth dynamics of the hypha of valsa mali in xylem. Test the effects of continual rain, back flow of nutrition from roots to top and ages of pruning wounds on the growth of the fungi in xylem and on the epidemics of the disease. Develop models to describe the relation-ship between the factors and the disease epidemics. Understand, with the help of molecular biological techniques, the genes and enzymes involved in growth of the pathogen in xylem. The research results will help to understand epidemics of the disease, to develop new techniques to forecast and control the disease epidemics, and to develop new fungicides.

苹果树腐烂病(Valsa mali)与其他病害不同，病菌侵染不是影响发生与流行的关键环节，而表皮内潜伏病菌穿透木栓层进入皮层和木质部内菌丝生长扩展是决定腐烂病发生与流行的关键环节，所有因子都通过影响这两个环节影响病害的发生与流行。本项目针对这两个特定环节，重点研究低温冻害、树势、干旱失水三个环境因子对腐烂病发生流行的影响，明确其间的量化关系；借助组织观察和分子生物学技术，了解病菌穿透木栓层的过程，解析与病菌穿透木栓层相关的酶类和基因,揭示流行因子对病菌穿透木栓层的影响机制； 研究掌握腐烂病菌菌丝在木质部内周年的生长扩展动态，明确连续阴雨、春季根部养份回流、剪锯口的龄期对木质部内病菌生长扩展和病害流行的数量影响；借助分子生物学手段，明确木质部内影响病菌生长的酶类和基因。研究结果将为深入理解苹果树腐烂病的发生流行规律提供理论依据，为苹果腐烂病防控技术、测报方法和防治药剂提供技术参考。

腐烂病(Valsa mali)是苹果树上的第一大病害，可造成死枝、死树和毁园。腐烂病的发生与流行不同于其他病害，病菌主要通过两条途径侵入皮层活体组织致病：.剪锯口是腐烂病菌侵染的一条重要途径。组织学观察发现，腐烂病菌主要从剪锯口的木质部侵染。随孢子悬浮液接种到剪锯口上的孢子，可被吸入导管，利用导管内的湿度和营养萌发，而不需额外湿度；在5-35℃下接种，木质部内都能检测到病菌，20℃下组织染菌率最高。腐烂病菌从剪锯口侵染后可沿导管纵向生长，沿木射线横向扩展，并能穿过微孔进入相邻导管。侵染初期病菌在木质部内的生长速度每天不短于0.5cm，最快超过1cm，明显快于皮层内病斑扩展速度。腐烂病菌能利用导管输导的水溶性营养和木质部的结构组份生长。腐烂病菌侵入木质部4小时后，β-1,4-内切葡聚糖酶基因表达量明显升高，但72小时后恢复原水平。5-35℃下病菌都能在木质部内生长， 30℃下最快；病菌在多年生枝条木质部内生长速度慢；当枝条的相对含水量低于90%时，病菌的生长速度明显减缓。自然条件下病菌在木质部内的生长主要受温度影响。腐烂病菌能从木质部进入皮层，也能从皮层进入木质部，木质部内生长存活的病菌是导致旧病斑复发的主要原因。.从枝干表层侵染是腐烂病菌侵染的另一条途径。组织学观测结果表明，腐烂病菌能够在枝干表层和伤口死组织内生长潜伏，但不能突破栓皮层侵入活体皮层组织致病。用分生孢子喷淋接种的苹果树6个月后，六个部位的带菌率都高于80%。苹果枝干皮层的浸出液能促进病菌孢子的萌发生长，病菌孢子萌发。离体条件下，腐烂病菌孢子在10-35℃的范围内都能萌发，最适25℃；病菌孢子萌发需要高于90%的相对湿度；在适宜条件下病菌孢子12小时内可萌发产生菌丝, 48小时后菌丝长度达156μm。愈合后6个月的伤口、果柄痕易感腐烂病，但腐烂病菌不能从皮孔侵染。发育不良或未成熟的枝条受冻后易感染腐烂病；-10℃以下的冷冻、冰冻、失水干燥都显著增加枝干对腐烂病的敏感性。