Vrålstad Trude, Fossheim Tonje, Schumacher Trond
1 Ascomycete Research Group, Oslo, Norway (ARON), Department of Biology, University of Oslo, PO Box 1045 Blindern, N-0316 Oslo, Norway.
New Phytol. 2000 Mar;145(3):549-563. doi: 10.1046/j.1469-8137.2000.00605.x.
The mycobionts of Piceirhiza bicolorata, a distinct ectomycorrhizal morphotype of conifers and hardwoods, have been identified by internal transcribed spacer 1 (ITS1) nuclear ribosomal DNA (rDNA) sequence comparison of the fungi involved. Samples of Piceirhiza bicolorata were obtained from seedlings of Picea abies, Pinus sylvestris, Betula pubescens, Populus tremula, Quercus robur and Salix phylicifolia. In an initial screening, the fungus amplified with universal ITS primers from ectomycorrhizal root samples of P. bicolorata shared approx. 95% ITS1 sequence identity with the ericoid mycorrhizal fungus Hymenoscyphus ericae. A total of 77 out of 88 (= 87.5%) DNA samples (i.e. 52/56 root samples and 25/32 axenic culture isolates) of P. bicolorata were successfully amplified with a taxon-selective primer designed for exclusive amplification of H. ericae-like strains. Forty-seven amplicons were sequenced, yielding 15 different ITS1 genotypes that differed by 1-14 nucleotide character state changes. An inferred ITS1 phylogeny (maximum parsimony) showed that a single major evolutionary lineage of P. bicolorata embraced the historically important H. ericae isolates in a 100% bootstrap-supported clade. The 15 P. bicolorata genotypes were positioned in four subclades, roughly corresponding to morphological groups of P. bicolorata isolates observed in axenic culture. Culture isolates of H. ericae and P. bicolorata share some common morphological features including slow, dense growth and formation of short aerial hyphal aggregates. Our results suggest that members of the H. ericae aggregate participate in the formation of the distinct ectomycorrhizal morphotype P. bicolorata. This opposes the widely accepted discrimination of ericoid and ectomycorrhizal mycobionts of the boreal forest ecosystem. The high prevalence of the P. bicolorata morphotype on pioneer seedlings of P. sylvestris, B. pubescens and S. phylicifolia at a copper mine spoil was remarkable. Hypotheses of possible nutrient mobilization and detoxification potentials of the fungal associates of P. bicolorata are discussed. We hypothesize that ericoid and ectomycorrhizal plants may share mycobionts of the H. ericae aggregate.
双色云杉根瘤菌（Piceirhiza bicolorata）是针叶树和阔叶树独特的外生菌根形态类型，通过对相关真菌的内部转录间隔区1（ITS1）核糖体DNA（rDNA）序列比较，已鉴定出其菌根真菌。双色云杉根瘤菌的样本取自欧洲云杉（Picea abies）、欧洲赤松（Pinus sylvestris）、毛桦（Betula pubescens）、欧洲山杨（Populus tremula）、夏栎（Quercus robur）和柳叶菜柳（Salix phylicifolia）的幼苗。在初步筛选中，用通用ITS引物从双色云杉根瘤菌外生菌根根样本中扩增出的真菌，其ITS1序列与石楠状菌根真菌欧石楠小皮伞（Hymenoscyphus ericae）约有95%的序列同一性。在88个双色云杉根瘤菌DNA样本（即56个根样本中的52个和32个无菌培养分离物中的25个）中，共有77个（=87.5%）成功地用专为欧石楠小皮伞样菌株特异性扩增设计的分类群选择性引物进行了扩增。对47个扩增子进行了测序，产生了15种不同的ITS1基因型，它们在1 - 14个核苷酸特征状态变化上存在差异。推断的ITS1系统发育（最大简约法）表明，双色云杉根瘤菌的一个主要进化谱系在一个100%自展支持的分支中包含了具有历史重要性的欧石楠小皮伞分离物。这15种双色云杉根瘤菌基因型位于四个亚分支中，大致对应于在无菌培养中观察到的双色云杉根瘤菌分离物的形态学组。欧石楠小皮伞和双色云杉根瘤菌的培养分离物具有一些共同的形态特征，包括生长缓慢、密集以及形成短的气生菌丝聚集体。我们的结果表明，欧石楠小皮伞聚集体的成员参与了独特的外生菌根形态类型双色云杉根瘤菌的形成。这与北方森林生态系统中石楠状菌根和外生菌根菌根真菌被广泛接受的区分相悖。在一个铜矿废石场上，双色云杉根瘤菌形态类型在欧洲赤松、毛桦和柳叶菜柳的先锋幼苗上的高发生率引人注目。讨论了双色云杉根瘤菌真菌共生体可能的养分动员和解毒潜力的假设。我们推测石楠状菌根植物和外生菌根植物可能共享欧石楠小皮伞聚集体的菌根真菌。
