Phytosanitary assessment of black and grey alder stands in Latvia

Black alder <i>Alnus glutinosa</i> (L.) Gaertn. and grey alder <i>Alnus incana</i> (L.) Moench, cover up to 11% of the forest area in Latvia. As alder dieback caused mainly by <i>Phytophthora</i> has been reported in several countries, we aimed to assess the distribution of <i>Phytophthora</i>-like symptomatic alders in Latvia and surveyed 208 alder-dominated forest stands. Symptomatic alders were found in 28% of stands, and in 8% of stands, the infected tree proportion comprised more than 10% of trees. Pocket Diagnostics® tests confirmed <i>Phytophthora</i> or other oomycete infection in 13% of stands, mainly in Central and Eastern Latvia. Trees that tested positive were mainly grey alder (1.0% of the overall number of surveyed grey alders), and fewer black alders tested positive (0.2% of the overall number of surveyed black alders). Grey alder had a significantly higher probability of having symptoms at both the stand level (probability 0.429) and the individual tree level (probability 0.017) in comparison to black alder (probabilities 0.185 and 0.004, respectively). In conclusion, alders with <i>Phytophthora</i>-like symptoms were found throughout the territory of Latvia, however, infection risk for the economically important tree species black alder is low.

黑桤木（*Alnus glutinosa* (L.) Gaertn.）与灰桤木（*Alnus incana* (L.) Moench）的分布面积占拉脱维亚森林总面积的11%。鉴于由疫霉属（Phytophthora）引发的桤木枯梢病已在多个国家被报道，本研究旨在评估拉脱维亚境内表现出疑似疫霉属病害症状的桤木分布情况，共调查了208个以桤木为优势树种的林分。结果显示，28%的林分内发现了表现病害症状的桤木；其中8%的林分中，感病树木占总林木比例超过10%。通过Pocket Diagnostics®试剂盒检测，13%的林分被证实存在疫霉属或其他卵菌（oomycete）感染，感染区域主要集中在拉脱维亚中部与东部。检测呈阳性的植株以灰桤木为主，占调查灰桤木总数的1.0%；黑桤木阳性占比更低，仅为调查黑桤木总数的0.2%。相较于黑桤木（林分水平感病概率为0.185，单木水平感病概率为0.004），灰桤木在林分水平（感病概率0.429）与单木水平（感病概率0.017）的感病概率均显著更高。研究结论表明，疑似疫霉属病害的桤木在拉脱维亚全境均有分布，但作为经济价值重要的树种，黑桤木的感染风险较低。