大豆疫霉和苜蓿疫霉rDNA ITS序列分析*

采用真菌核糖体基因转录间隔区(ITS)通用引物,PCR分别扩增了Phytophthora sojae的5个菌株(Pg1、Pg2、Pg3、CN1和S317)和1个P. medicaginis (菌株44390)的ITS1与ITS2,并对PCR产物进行了序列测定。根据Bioedit软件中的neighbour-joining methods分析法将上述序列和Genbank中已登录的P. sojae、P. medicaginis、P. megasperma和P.trifolii等4个形态学种10个登录菌株的ITS1与ITS2碱基序列进行聚类分析。结果是聚类组与形态学种有一定差别,4个种16个菌株分成7个聚类组。结果表明,分别属于同一形态学种且可聚为一组的不同个体之间的ITS碱基序列遗传相似性最高,但是也具有一定的多样性;形态学上属于不同种的个体的ITS可以聚为一组。上述结果提示L41385可能不属于P. sojae, L41380可能属于是P. trifolii,P. megasperma仍是一个复合种。同时提示ITS DNA碱基序列可以区分形态学种。

SEQUENCE ANALYSIS OF ITS OF THE RIBOSOMAL RNA GENE REPEAT OF PHYTOPHTHORA SOJAE AND P. MEDICAGINIS

The internal transcribed spacer regions (ITS1 and ITS2) of the ribosomal RNA gene from five isolates of Phytophthora sojae (Pg1, Pg2, Pg3, CN1 and S317) and an isolate, 44390 of P. medicaginis were amplified using the polymerase chain reaction and sequenced. Sequences from the above isolates were compared with published sequences of P. sojae (Accession No.: AF228089, AF266769 and L41385), P. medicaginis (Accession No.: L41379 and AF266799), P. megasperma (Accession No.: L41380, L41381, L41382 and AF266794) and P. trifolii (Accession No.: AF266800) in Genbank database and phylogenetic trees were produced based on ITS sequence data by 揘eighbour-joining?methods of the software Bioedit. The resultant grouping of species differed from groupings established using classical morphological and biological characteristics. One group comprised all P. sojae isolates excepted L41385. The isolate tested 44390, AF266799 and L41379 were clustered into the second group P. medicaginis. The third group consisted of two isolates of two species from Genbank, AF266800 (P. trifolii) and L41380 (P. megasperma). The isolate L41381 (P. megasperma), L41382 (P. megasperma), AF266794 (P. megasperma) became the fourth group. L41385 was separated from its morphological species to become the firth group. The results showed that ITS sequences of different isolate of the same phylogenetic group within one morphological species were polymorphic. The results further indicated that L41385 (the accession No. for Genbank database) could not obviously belong to P. sojae and L41380, one isolate of P. megasperma might belong to P. trifolii. Moreover the species P. megasperma may be a Phytophthora complex. It suggested that the sequence difference within ITS could provide a characteristic for distinguishing morphological Phytophthora species.