Ganthaler Andrea, Trujillo-Moya Carlos, Burger Stefanie, Hlavaty Juraj, Kummer Stefan, Tschulenk Waltraud, Walter Ingrid
Department of Botany, University of Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria.
Department of Forest Growth, Silviculture & Genetics, Austrian Research Centre for Forests BFW, Seckendorff-Gudent-Weg 8, 1131 Vienna, Austria.
Tree Physiol. 2025 Jul 1;45(7). doi: 10.1093/treephys/tpaf066.
Infection of Norway spruce (Picea abies L.) by the rust Chrysomyxa rhododendri is a major problem in European subalpine forests, causing severe defoliation and reduced growth. However, as with most pathogens from high-elevation environments, little is known about the host-pathogen interaction, the associated plant cellular damage and responses, and their differential expression in susceptible and resistant host trees. Here we report on the development of the biotrophic pathogen in the host tissues, from infection by basidiospores to release of aeciospores, by analysing needles at different time points after infection by histology and transmission electron microscopy. Ultrastructural changes in the host cells, ranging from cell reorganization and degradation to the accumulation of secondary compounds, were localized and characterized in both susceptible and a resistant genotype. Chrysomyxa rhododendri formed a dense mycelium in the intercellular spaces of the needle mesophyll of susceptible trees, followed by the formation of subepidermal spermogonia and aecia. Symptomatic needle yellowing corresponded to the spatial expansion of the mycelium and was caused by degradation, but not collapse, of the mesophyll cells with chloroplasts. In needles of the enhanced resistant genotype, only few fungal hyphae appeared, but distinct modifications of the cell walls and an accumulation of electron dense material in the intercellular space appeared. In addition, large tannin droplets were observed around fungal structures, indicating an increased accumulation of polyphenols. The findings are consistent with observations on other heterocyclic rusts and with known physiological and molecular responses of infected trees, including a reduced photosynthetic activity, changes in the needle phenolic profile and a local hypersensitive response. Highly resistant trees may be able to limit fungal growth and associated damage by rapidly enhancing structural and chemical barriers in the needle mesophyll.
欧洲云杉（Picea abies L.）被杜鹃金锈菌（Chrysomyxa rhododendri）感染是欧洲亚高山森林中的一个主要问题，会导致严重落叶和生长减缓。然而，与大多数来自高海拔环境的病原体一样，对于宿主 - 病原体相互作用、相关的植物细胞损伤和反应，以及它们在易感和抗性宿主树中的差异表达知之甚少。在这里，我们通过组织学和透射电子显微镜分析感染后不同时间点的针叶，报告了活体营养型病原体在宿主组织中的发育情况，从担孢子感染到锈孢子释放。在易感和抗性基因型中，均定位并表征了宿主细胞的超微结构变化，范围从细胞重组和降解到次生化合物的积累。杜鹃金锈菌在易感树针叶叶肉的细胞间隙中形成致密菌丝体，随后形成表皮下性孢子器和锈孢子器。有症状的针叶变黄与菌丝体的空间扩展相对应，是由叶绿体叶肉细胞的降解而非崩溃引起的。在增强抗性基因型的针叶中，仅出现少数真菌菌丝，但出现了细胞壁的明显修饰以及细胞间隙中电子致密物质的积累。此外，在真菌结构周围观察到大量单宁液滴，表明多酚积累增加。这些发现与对其他异环锈菌的观察结果一致，也与受感染树木已知的生理和分子反应一致，包括光合活性降低、针叶酚类特征变化和局部过敏反应。高抗性树木可能能够通过迅速增强针叶叶肉中的结构和化学屏障来限制真菌生长及相关损害。
