• There are no records of established plant pathogenic Phytophthora species in Finnish forests, but they are likely in the future. Therefore, the effects of Phytophthora inoculations on young, ca. 2‐month‐old silver birch (Betula pendula) seedling roots and shoots were investigated.
• Visual inspection of dark discoloration, direct PCR and re‐isolation, and detailed root morphology analyses were used to evaluate the effects of Phytophthora inoculation on roots. Symptoms in leaves and stems were also recorded.
• Phytophthora was successfully re‐isolated from 67% of the surface‐sterilized roots of inoculated seedlings, but not from the non‐inoculated control seedlings. Dark discolorations were found more often in the root segments of inoculated seedlings than in control seedlings. In the Phytophthora‐treated seedlings, discoloured root segments were usually linked and found primarily in the main root or lateral roots attached to it, whereas in the control seedlings a few single discoloured root segments were scattered throughout the root systems. The number of root segments was lower in the inoculated than in the control seedlings, indicating root loss after Phytophthora inoculation. In the shoots of inoculated birches, leaf and shoot wilting was observed.
• The appearance of wilting in shoots without visible dark discoloration in the base of stems indicated that symptoms originated from roots inoculated with Phytophthora.

中文翻译：

---

疫霉疫霉菌感染后白桦的根变色和枝条症状

• 芬兰森林中没有确定的植物致病疫霉菌种的记录，但将来可能会出现。因此，疫霉菌接种对幼虫的影响。研究了2个月大的白桦（Betula pendula）幼苗的根和芽。
• 目视检查深色变色，直接PCR和重新分离，以及详细的根系形态分析，以评估疫霉菌接种对根系的影响。还记录了叶和茎的症状。
• 疫霉菌已成功地从接种苗表面消毒的根的67％中重新分离，但未从未接种对照苗中重新分离出来。在接种的幼苗的根部中比对照幼苗更经常发现暗色。在疫霉菌处理过的幼苗中，变色的根段通常是连锁的，主要存在于与其相连的主根或侧根中，而在对照幼苗中，一些单个变色的根段散布在整个根系中。接种后的根段数少于对照幼苗，表明疫霉菌接种后根系流失。在接种的桦树的芽中，观察到叶和芽枯萎。
• 枝条上出现枯萎现象，茎基部没有明显的深色变色，这表明症状源于接种疫霉的根。