Analysis of host exponsion sorategy of the Erysiphales using moleculor phylogenetic techniques

1.基于核糖体DMA核苷酸序列的系统发育分析表明，白粉病真菌可分为5个主要谱系。分生孢子阶段的形态很好地界定了各自的谱系，但没有确定子囊的形态。在这个真菌类群中，树寄生类群通常是祖先，并且在各自的谱系中发生了多次从树木到草本植物的宿主扩展。随着寄主向草本植物的扩展，附属物形态发生了多次简化。简单的菌丝体附属物是聚合的结果。详细研究了囊藻科寄主的扩展途径。Sphaerotheca属的两个分支分别来自于Podosphaera属。Magnicellulatae是由寄生于蔷薇科Prunus（蔷薇科）的Podosphaera种衍生而来，获得了寄生于Scrophulariaceae的寄生，然后扩展到Asteraceae的寄主范围。在对菊科植物进行遗传辐射后，它们进一步将寄主范围扩展到其他植物科。根据Berbee和Taylor（2001）报道的分子钟（1.26%/100 myr），计算得出丹毒科和黏液科的分裂和丹毒科内部的首次分化分别发生在100 myr和76 myr之前。在本研究分析的Golovinomyces分类群中，鉴定出5个主要类群，每个类群均由来自Asteraceae单一部落的分离物代表。4个类群的寄主植物严格局限于菊科。第五类群为乳状菌科（Lactuceae），是一个由菊科乳状菌科（Lactuceae）和其他所有植物科的分离物组成的大类群，这表明Golovinomyces与菊科在其进化的早期阶段有着密切的亲缘关系。我们认为戈洛维菌的宿主-寄生虫关系在进化史上有两个不同的阶段。一个阶段是与寄主植物发育相适应的分化，这种分化发生在菊科植物中。另一个阶段是寄主跳迁，发生在菊科和其他科之间。少

1.Phylogenetic analyses based on the nucleotide sequences of the nuclear ribosomal DMA revealed that the powdery mildew fungi are divided into five major lineages. The respective lineage was well defined by the morphology of conidial stage, but not of ascomata. In this fungal group, tree-parasitic taxa are generally ancestral, and multiple times of host expansion from trees to herbs have occurred within the respective lineage. Accompanying with the host expansion to herbs, simplification of appendage morphology has occurred multiple times. The simple, mycelioid appendages are thus a result of convergence. Host expansion route was investigated in detail in the tribe Cystotheceae. Two sections of the genus Sphaerotheca were derived from the genus Podosphaera separately. The section Magnicellulatae was derived from a Podosphaera species parasitic to Prunus (Rosaceae), acquired parasitism to the Scrophulariaceae, and then expanded host range into the Asteraceae. After genetic radiation on … More the Asteraceae, they further expanded their host ranges into other plant families. According to the molecular clock (1.26%/100 myr) reported by Berbee and Taylor (2001), splitting of the Erysiphales and the Myxotrichaceae and first divergence within the Erysiphales was calculated to have occurred 100 and 76 myr ago, respectively.2.Five major groups, each represented by isolates from a single tribe of the Asteraceae, were identified in Golovinomyces taxa analyzed in this study. Host plants of four groups were strictly restricted to the Asteraceae. The fifth group, the Lactuceae group, is a large group composed of isolates collected from the tribe Lactuceae of the Asteraceae and all other plant families, which suggests a close affinity between Golovinomyces and the Asteraceae in the early stages of their evolution. We suggest that there are two different phases in the evolutionary history of the host-parasite relationships of Golovinomyces. One phase is divergence in accord with the phytogeny of their hosts, which occurred within the Asteraceae. The another phase is host-jumping, which occurred from the Asteraceae to other families and within the Asteraceae. Less