北京地区桃黑斑病新症状的发现与诊断

2019年-2020年在北京地区桃园病害调研普查时发现一种桃树病害的新发症状-新叶坏死，主要症状表现为当年新生枝条顶端新叶和生长点腐烂坏死。为明确这种新叶坏死症状是否由病原菌侵染引起，从北京平谷2个乡镇3个桃园采集35份病梢样品，经病样组织分离和菌株纯化，选取12个代表性菌株进行形态学鉴定、系统进化分析以及致病性测定。结果显示，通过形态学鉴定和多基因(ITS,Alt a1,gpd)系统发育分析，以上分离株均鉴定为链格孢Alternaria alternata;3株代表性菌株的致病性测定验证了A.alternata是引起新叶坏死症状的病原菌，并且该病原菌也能导致桃枝条和果实发病，产生黑斑病症状。这是首次报道A.alternata除了引起桃果实黑斑症状之外，还可以引起桃树新叶坏死症状，结果进一步丰富了链格孢侵染桃树的症状多样性，为链格孢引起的病害的整体防控提供了理论基础。

Occurrence and diagnosis of new symptoms of peach black spot disease in Beijing

A new young leaf necrosis symptom was observed in peach orchards located in Beijing during 2019-2020: brown rot spots on growing tips and new leaves of young shoots. To determine whether the symptom is caused by pathogenic infection, 35 samples were collected from three peach orchards in two towns of Pinggu, Beijing. After pathogen isolation, twelve representative fungal isolates were identified as Alternaria alternata according to morphological characteristics and multi gene (ITS, Alt a1, gpd) phylogenetic analysis. Pathogenicity assay of three representative isolates confirmed that A. alternata was the causal agent of young leaf necrosis symptom. It also caused black spot symptom on twigs and fruits. Our study provides new evidences for the symptoms caused by A. alternate and a new theoretical basis for integrated control of this disease.