Johnson Jason A, Harrington Thomas C, Engelbrecht C J B
Department of Plant Pathology, Iowa State University, Ames 50010, USA.
Mycologia. 2005 Sep-Oct;97(5):1067-92. doi: 10.3852/mycologia.97.5.1067.
Ceratocystis fimbriata is a widely distributed, plant pathogenic fungus that causes wilts and cankers on many woody hosts. Earlier phylogenetic analyses of DNA sequences revealed three geographic clades within the C. fimbriata complex that are centered respectively in North America, Latin America and Asia. This study looked for cryptic species within the North American clade. The internal transcribed spacer regions (ITS) of the rDNA were sequenced, and phylogenetic analysis indicated that most isolates from the North American clade group into four host-associated lineages, referred to as the aspen, hickory, oak and cherry lineages, which were isolated primarily from wounds or diseased trees of Populus, Carya, Quercus and Prunus, respectively. A single isolate collected from P. serotina in Wisconsin had a unique ITS sequence. Allozyme electromorphs also were highly polymorphic within the North American clade, and the inferred phylogenies from these data were congruent with the ITS-rDNA analyses. In pairing experiments isolates from the aspen, hickory, oak and cherry lineages were interfertile only with other isolates from their respective lineages. Inoculation experiments with isolates of the four host-associated groupings showed strong host specialization by isolates from the aspen and hickory lineages on Populus tremuloides and Carya illinoensis, respectively, but isolates from the oak and cherry lineages did not consistently reveal host specialization. Morphological features distinguish isolates in the North American clade from those of the Latin American clade (including C. fimbriata sensu stricto). Based on the phylogenetic evidence, interfertility, host specialization and morphology, the oak and cherry lineages are recognized as the earlier described C. variospora, the poplar lineage as C. populicola sp. nov., and the hickory lineage as C. caryae sp. nov. A new species associated with the bark beetle Scolytus quadrispinosus on Carya is closely related to C. caryae and is described as C. smalleyi.
帚状炭疽菌是一种广泛分布的植物病原真菌，可在许多木本寄主上引起枯萎病和溃疡病。早期对DNA序列的系统发育分析揭示了帚状炭疽菌复合体内的三个地理分支，分别以北美、拉丁美洲和亚洲为中心。本研究在北美分支中寻找隐存种。对核糖体DNA的内部转录间隔区（ITS）进行了测序，系统发育分析表明，北美分支的大多数分离株分为四个寄主相关谱系，分别称为白杨、山核桃、橡树和樱桃谱系，它们主要分别从杨树、山核桃、栎树和李树的伤口或患病树木中分离得到。从威斯康星州的黑樱桃中采集的一个分离株具有独特的ITS序列。等位酶电变体在北美分支内也具有高度多态性，从这些数据推断的系统发育与ITS-rDNA分析一致。在配对实验中，白杨、山核桃、橡树和樱桃谱系的分离株仅与各自谱系的其他分离株可育。对四个寄主相关分组的分离株进行接种实验表明，白杨和山核桃谱系的分离株分别对颤杨和伊利诺伊州山核桃表现出强烈的寄主专化性，但橡树和樱桃谱系的分离株并未始终表现出寄主专化性。形态特征将北美分支的分离株与拉丁美洲分支的分离株（包括狭义的帚状炭疽菌）区分开来。基于系统发育证据、可育性、寄主专化性和形态学，橡树和樱桃谱系被认定为较早描述的多变炭疽菌，杨树谱系为新种杨树炭疽菌，山核桃谱系为新种山核桃炭疽菌。一种与山核桃上的四刺小蠹相关的新物种与山核桃炭疽菌密切相关，被描述为斯氏炭疽菌。
