Department of Biology, University of Ottawa, Ottawa, ON, K1N 6N5, Canada.
Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON, K1A 0C6, Canada.
New Phytol. 2024 May;242(4):1771-1784. doi: 10.1111/nph.19121. Epub 2023 Jul 11.
Rhizophagus irregularis is the model species for arbuscular mycorrhizal fungi (AMF) research and the most widely propagated species for commercial plant biostimulants. Using asymbiotic and symbiotic cultivation systems initiated from single spores, advanced microscopy, Sanger sequencing of the glomalin gene, and PacBio sequencing of the partial 45S rRNA gene, we show that four strains of R. irregularis produce spores of two distinct morphotypes, one corresponding to the morphotype described in the R. irregularis protologue and the other having the phenotype of R. fasciculatus. The two spore morphs are easily distinguished by spore colour, thickness of the subtending hypha, thickness of the second wall layer, lamination of the innermost layer, and the dextrinoid reaction of the two outer spore wall layers to Melzer's reagent. The glomalin gene of the two spore morphs is identical and that of the PacBio sequences of the partial SSU-ITS-LSU region (2780 bp) obtained from single spores of the R. cf fasciculatus morphotype has a median pairwise similarity of 99.8% (SD = 0.005%) to the rDNA ribotypes of R. irregularis DAOM 197198. Based on these results, we conclude that the model AMF species R. irregularis is dimorphic, which has caused taxonomic confusion in culture collections and possibly in AMF research.
粗糙球囊霉是丛枝菌根真菌（AMF）研究的模式种，也是商业植物生物刺激素中最广泛传播的种。我们使用从单个孢子启动的非共生和共生培养系统、先进的显微镜技术、胶结蛋白基因的 Sanger 测序以及部分 45S rRNA 基因的 PacBio 测序，表明四种粗糙球囊霉菌株产生两种不同形态的孢子，一种与粗糙球囊霉原描述的形态类型相对应，另一种具有密集球囊霉的表型。这两种孢子形态很容易通过孢子颜色、下伏菌丝的厚度、第二层细胞壁的厚度、最内层的分层以及两层最外层孢子壁对梅尔泽试剂的糊精反应来区分。两种孢子形态的胶结蛋白基因相同，从密集球囊霉形态的单个孢子获得的部分 SSU-ITS-LSU 区（2780 bp）PacBio 序列的 glomalin 基因与粗糙球囊霉 DAOM 197198 的 rDNA 核糖体类型具有 99.8%（SD=0.005%）的中位数成对相似性。基于这些结果，我们得出结论，模式 AMF 物种粗糙球囊霉是二态的，这在培养物收集和可能在 AMF 研究中引起了分类混淆。
