Department of Environmental Science and Engineering, Ishikawa Prefectural University, Nonoichi-cho, Ishikawa, Japan.
Plant Signal Behav. 2010 Apr;5(4):415-8. doi: 10.4161/psb.5.4.10834. Epub 2010 Apr 2.
Aciculosporium take causes continuous shoot growth but maintains normal leaf-arrangement and branching patterns in the host plant, which eventually resulting in witches' broom disease of bamboo. An in situ hybridization technique with a species-specific oligonucleotide probe was recently used to demonstrate that endophytic mycelia of A. take is predominantly distributed in the intercellular spaces of the shoot apical meristem of the host. Endophytic hyphae in meristematic tissues, which may produce auxin, are responsible for continuous primordium initiation within the shoot apex. Here I examine another bamboo witches' broom causal fungus, Heteroepichloë sasae. Both species are biotrophic and belong to family Clavicipitaceae: however, H. sasae does not cause continuous shoot growth. Histological study showed that H. sasae mycelia were distributed superficially, even on shoot apical meristems. These observations suggest that when their stromata develop, endophytic A. take destroys shoot apical meristem and epiphytic H. sasae chokes the shoot apex of the host. Stromata formation consequently causes lateral bud outgrowth because of release from apical dominance. This process repeats and eventually results in the witches' broom symptoms.
密枝凸脐孢引起竹子的连续芽生长，但维持了宿主植物正常的叶序和分枝模式，最终导致竹子丛枝病。最近，一种使用种特异性寡核苷酸探针的原位杂交技术被用于证明 A. take 的内生菌丝主要分布在宿主茎尖分生组织的细胞间隙中。分生组织中的内生菌丝可能产生生长素，负责在茎尖内连续启动原基。在这里，我研究了另一种竹子丛枝病的致病真菌，异旋孢腔菌。这两个物种都是生物营养型的，属于棒束孢科：然而，H. sasae 不会引起连续芽生长。组织学研究表明，H. sasae 的菌丝分布在表面，甚至在茎尖分生组织上。这些观察结果表明，当它们的菌核发育时，内生的 A. take 破坏茎尖分生组织，外生的 H. sasae 则阻塞宿主的茎尖。因此，菌核的形成导致侧芽的生长，因为顶端优势被解除。这个过程不断重复，最终导致丛枝病的症状。
