Witches’ broom of birch (Betula spp.) caused by Taphrina betulina is an understudied disease that causes the formation of woody tumours, from which ectopic axillary buds and branches grow to form a broom-like structure. We have addressed two aspects of this disease using naturally infected mature trees in the field. Broom symptoms offer a convenient means of scoring susceptibility in the field. Variation in broom symptom presentation suggests possible variation in resistance against witches’ broom disease. We tracked the local distribution of susceptible individuals among 721 trees at 159 independent sites. The analysis supports the hypothesis that there was genetic resistance segregating in these birch populations. Anatomical changes in broom symptom bearing branches of European silver birch (Betula pendula) were also addressed by comparing sections of tissues from three locations in the same branch, which were normal, swollen in infected tissue adjacent to a tumour, and inside a tumour. Examination of tumours revealed disorganized and swollen xylem, expanded secondary phloem and expanded periderm. Swollen tissues newly infected from spreading disease adjacent to tumours exhibited enhanced growth only in secondary phloem and the periderm, which also exhibited distortions. This finding suggests that tumour formation and possibly pathogen colonization may initiate in these tissues.

中文翻译：

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Taphrina betulina感染桦树的遗传抗性和肿瘤形态

由Taphrina betulina引起的白桦树 ( Betula spp.) 的女巫扫帚是一种引起木本肿瘤形成的未充分研究的疾病，异位腋芽和枝条从中生长形成扫帚状结构。我们已经在田间使用自然感染的成熟树木解决了这种疾病的两个方面。扫帚症状提供了一种方便的方法来评估该领域的易感性。扫帚症状表现的变化表明对女巫扫帚病的抵抗力可能有所不同。我们跟踪了 159 个独立地点的 721 棵树中易感个体的局部分布。该分析支持了在这些桦树种群中存在遗传抗性分离的假设。欧洲白桦（Betula pendula）带扫帚症状的解剖学变化) 还通过比较同一分支中三个位置的组织切片来解决，这些组织切片是正常的，在邻近肿瘤的受感染组织中肿胀，以及在肿瘤内部。肿瘤检查显示木质部无组织且肿胀，次生韧皮部扩张，周皮扩张。因肿瘤附近传播疾病而新感染的肿胀组织仅在次生韧皮部和周皮中表现出增强的生长，这些组织也表现出扭曲。这一发现表明肿瘤形成和可能的病原体定植可能在这些组织中开始。