基于rDNA ITS序列探讨部分腐霉种的系统发育与其形态特征

基于对73株计58种腐霉和6种疫霉的核糖体DNA的ITS序列分析,以海生疫霉为外围群,按邻接法构建系统发育树,对腐霉的系统发育关系进行了研究。结果表明:在58种腐霉中,Pythium ostracodes,P.chamaehyphon,P.carbonicum,P.montanum和P.vexans归为同一组,介于其它腐霉和疫霉之间,这5种腐霉的孢子囊均为球形;现已归为疫霉属的P.undulatum 单独为一组,它与腐霉的亲缘关系比疫霉更近;其余52种腐霉聚成一大组,这52种腐霉基本上按孢子囊或菌丝膨大体形态分成Ⅰ、Ⅱ两组:第1组31种腐霉, 其中30种腐霉的孢子囊或菌丝膨大体为球形;第Ⅱ组21种腐霉,其中19种腐霉的孢子囊为丝状、瓣状或裂片状。基于ITS序列分析,腐霉属的其它性状如藏卵器壁是否光滑、卵孢子是否满器、雄器的着生方式和数量、异宗配合等呈多元演化。

PHYLOGENETIC RELATIONSHIPS AND ITS MORPHOLOGICAL CHARACTERISTICS AMONG SOME PYTHIUM SPECIES INFERRED FROM SEQUENCE ANALYSIS OF rDNA ITS

The sequences of rDNA ITS of 73 isolates representing 58 species of Pythium and 6 species of Phytophthora were analyzed to reconstruct their phylogenetic tree using neighbor-joining method and Halophytophthora batemanensis as an outgroup. Their phylogenetic relationships were studied. The present results showed that Pythium ostracodes, P. chamaehyphon grouped in a clade together with P. montanum, P. carbonicum and P. vexans, which were between other Pythium species and Phytophthora. The five species Pythium all produced spherical zoosporangia. Pythium undulation transferred into the genus Phytophthora (as Phytophthora undulatum) formed a single group. Its relationship was closer to the genus Pythium than Phytophthora. The rest 52 species Pythium gathered one big group. They were divided into two major clades that were, in a general sense, reflective of zoosporangial or hyphal swelling morphology. Clade Ⅰ was comprised of thirty-one species, thirty of which produced spherical zoosporangia or spherical hyphal swellings. Clade Ⅱ was comprised of twenty-one species, nineteen of which produced filamentous to lobulate zoosporangia. Characteristics such as oogonium ornamentation, antheridium attachment, number of antheridia, and heterothallism were polyphyletic, inferred from ITS sequence analysis.