Porras-Alfaro Andrea, Bayman Paul
Departamento de Biología, Universidad de Puerto Rico - Río Piedras, PO Box 23360, San Juan, Puerto Rico 00931.
Mycologia. 2007 Jul-Aug;99(4):510-25. doi: 10.3852/mycologia.99.4.510.
Mycorrhizal fungi are essential for the germination of orchid seeds. However, the specificity of orchids for their mycorrhizal fungi and the effects of the fungi on orchid growth are controversial. Mycorrhizal fungi have been studied in some temperate and tropical, epiphytic orchids, but the symbionts of tropical, terrestrial orchids are still unknown. Here we study diversity, specificity and function of mycorrhizal fungi in Vanilla, a pantropical genus that is both terrestrial and epiphytic. Mycorrhizal roots were collected from four Vanilla species in Puerto Rico, Costa Rica and Cuba. Cultured and uncultured mycorrhizal fungi were identified by sequencing the internal transcribed spacer region of nuclear rDNA (nrITS) and part of the mitochondrial ribosomal large subunit (mtLSU), and by counting number of nuclei in hyphae. Vanilla spp. were associated with a wide range of mycorrhizal fungi: Ceratobasidium, Thanatephorus and Tulasnella. Related fungi were found in different species of Vanilla, although at different relative frequencies. Ceratobasidium was more common in roots in soil and Tulasnella was more common in roots on tree bark, but several clades of fungi included strains from both substrates. Relative frequencies of genera of mycorrhizal fungi differed significantly between cultured fungi and those detected by direct amplification. Ceratobasidium and Tulasnella were tested for effects on seed germination of Vanilla and effects on growth of Vanilla and Dendrobium plants. We found significant differences among fungi in effects on seed germination and plant growth. Effects of mycorrhizal fungi on Vanilla and Dendrobium were similar: a clade of Ceratobasidium had a consistently positive effect on plant growth and seed germination. This clade has potential use in germination and propagation of orchids. Results confirmed that a single orchid species can be associated with several mycorrhizal fungi with different functional consequences for the plant.
菌根真菌对兰花种子的萌发至关重要。然而，兰花对其菌根真菌的特异性以及真菌对兰花生长的影响仍存在争议。已对一些温带和热带附生兰花中的菌根真菌进行了研究，但热带地生兰花的共生菌仍不为人知。在此，我们研究了香果兰属（一个兼具地生和附生习性的泛热带属）中菌根真菌的多样性、特异性和功能。从波多黎各、哥斯达黎加和古巴的四种香果兰属植物中采集了菌根。通过对核糖体DNA内转录间隔区（nrITS）和线粒体核糖体大亚基（mtLSU）的部分区域进行测序，并通过计算菌丝中的细胞核数量，对培养的和未培养的菌根真菌进行了鉴定。香果兰属植物与多种菌根真菌相关联：角担菌属、亡革菌属和胶膜菌属。在不同的香果兰属植物中发现了相关真菌，尽管相对频率不同。角担菌属在土壤中的根中更为常见，而胶膜菌属在树皮上的根中更为常见，但几个真菌分支包括来自两种基质的菌株。培养真菌与直接扩增检测到的真菌之间，菌根真菌属的相对频率存在显著差异。对角担菌属和胶膜菌属进行了对香果兰种子萌发的影响以及对香果兰和石斛属植物生长的影响的测试。我们发现不同真菌对种子萌发和植物生长的影响存在显著差异。菌根真菌对香果兰和石斛属植物的影响相似：一个角担菌属分支对植物生长和种子萌发始终具有积极影响。该分支在兰花的萌发和繁殖方面具有潜在用途。结果证实，单一兰花物种可与几种对植物具有不同功能影响的菌根真菌相关联。
