Department of Biology, University of Puerto Rico, Río Piedras, P.O. Box 23360, San Juan, Puerto Rico 00931-3360 USA.
Am J Bot. 2002 Nov;89(11):1852-8. doi: 10.3732/ajb.89.11.1852.
All orchids have an obligate relationship with mycorrhizal symbionts. Most orchid mycorrhizal fungi are classified in the form-genus Rhizoctonia. This group includes anamorphs of Tulasnella, Ceratobasidium, and Thanatephorus. Rhizoctonia can be classified according to the number of nuclei in young cells (multi-, bi-, and uninucleate). From nine Puerto Rican orchids we isolated 108 Rhizoctonia-like fungi. Our isolates were either bi- or uninucleate, the first report of uninucleate Rhizoctonia-like fungi as orchid endophytes. We sequenced the internal transcribed spacer (ITS) region of nuclear ribosomal DNA from 26 isolates and identified four fungal lineages, all related to Ceratobasidium spp. from temperate regions. Most orchid species hosted more than one lineage, demonstrating considerable variation in mycorrhizal associations even among related orchid species. The uninucleate condition was not a good phylogenetic character in mycorrhizal fungi from Puerto Rico. All four lineages were represented by fungi from Tolumnia variegata, but only one lineage included fungi from Ionopsis utricularioides. Tropical epiphytic orchids appear to vary in degree of specificity in their mycorrhizal interactions more than previously thought.
所有兰花都与菌根共生真菌有必然的关系。大多数兰花菌根真菌被分类为 Rhizoctonia 形式属。这一组包括 Tulasnella、Ceratobasidium 和 Thanatephorus 的无性型。Rhizoctonia 可以根据年轻细胞中的核数（多核、双核和单核）进行分类。从 9 种波多黎各兰花中，我们分离出了 108 种 Rhizoctonia 样真菌。我们的分离物要么是双核的，要么是单核的，这是首次报道单核 Rhizoctonia 样真菌作为兰花内生真菌。我们从 26 个分离物中测序了核核糖体 DNA 的内部转录间隔区（ITS），并鉴定出了 4 个真菌谱系，它们都与来自温带地区的 Ceratobasidium spp. 有关。大多数兰花物种宿主不止一个谱系，表明即使在相关的兰花物种中，菌根共生关系也存在相当大的变异。单核状态并不是波多黎各菌根真菌的一个良好的系统发育特征。所有四个谱系都有来自 Tolumnia variegata 的真菌代表，但只有一个谱系包括来自 Ionopsis utricularioides 的真菌。热带附生兰花在其菌根相互作用中的特异性程度上似乎比以前认为的更加多样化。
