Substantial growth losses in Douglas-fir can be the result of Swiss needle cast, a foliar disease caused by the fungus Nothophaeocryptopus gaeumannii. Although the disease is native to western North America, it is expected to become increasingly problematic in regions where climates become warmer in winter and wetter in spring, such as in coastal British Columbia (BC), Canada. Previous research suggests that tolerance to this disease is under partial genetic control. We therefore aim to screen for tolerance and resistance to the disease in the tree breeding population of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) in BC. We evaluated if early screening for resistance or tolerance to this disease is possible. We worked with 32 families grown for 18-years on two full-sibling genetic field trial sites representing different climates. We assessed >900 trees for disease signs and symptoms from 2017 to 2019. Needle retention was assessed in the field. In the laboratory, the proportion of stomata occluded with pseudothecia was measured, deoxyribonucleic acid (DNA) was extracted, and the proportion of fungal DNA in the needles was assessed using quantitative polymerase chain reaction. Strong differences were observed among families for needle retention, stomatal occlusion and fungal load. The milder and wetter site closer to the coast was generally more severely affected. Families showed rank changes between the two sites for all response variables. Higher needle retention was correlated with increased tree volume. No correlation was found between the proportion of stomata occluded with pseudothecia, fungal DNA load and needle retention. These results indicate that a more complex pathology is involved in causing needle loss. We conclude that screening for Swiss needle cast tolerance in the coastal BC Douglas-fir breeding population is possible if needle retention can be assessed and that area-specific deployment strategies may be needed given family rank changes in different environments.

中文翻译：

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瑞士对不列颠哥伦比亚省沿海道格拉斯冷杉繁殖种群的针刺耐受性

道格拉斯冷杉的大量生长损失可能是瑞士针叶草造成的，这是一种由真菌Nothophaeocryptopus gaeumannii引起的叶病。尽管该病原产于北美西部，但预计在冬季气候变暖和春季湿润的地区，例如加拿大不列颠哥伦比亚省（BC）沿海地区，问题将日益严重。先前的研究表明，对该病的耐受性处于部分遗传控制之下。因此，我们旨在筛选沿海道格拉斯冷杉（Pseudotsuga menziesii var。menziesii）树木育种种群对这种疾病的耐受性和抗性）。我们评估了是否有可能早期筛查对该病的耐药性或耐受性。我们与32个生长18年的家庭合作，在两个代表不同气候的全兄弟同基因田间试验场上工作。从2017年到2019年，我们评估了900多棵树木的疾病征兆和症状。在野外评估了针头保留率。在实验室中，测量了假性皮层阻塞的气孔比例，提取了脱氧核糖核酸（DNA），并使用定量聚合酶链反应评估了针中真菌DNA的比例。家庭之间在针头保留，气孔阻塞和真菌负荷方面观察到强烈差异。靠近海岸的温和湿润地区通常受到的影响更大。家庭显示所有响应变量在两个位点之间的等级变化。较高的持针量与树木体积增加有关。在假皮膜阻塞的气孔比例，真菌DNA负荷和针头保留之间未发现相关性。这些结果表明，导致针头丢失的原因涉及更复杂的病理。我们得出的结论是，如果可以评估针头的保持力，就可以在沿海不列颠哥伦比亚省道格拉斯冷杉的繁殖种群中进行瑞士针刺耐受性的筛查，并且考虑到不同环境中家庭等级的变化，可能需要针对特定​​地区的部署策略。