Search

The genus Aegilopscomprises approximately 25 diploid, tetraploid and hexaploid species, in which the genome types of all allopolyploids involve either U or D genome, or both of them, The internal transcribed spacer (ITS) region of 18S‐26S nuclear ribosomal DNA (rDNA) from 11 allopolyploid species and 7 related diploid species in the genus were directly sequenced by pooled PCR products. Phylogenetic analyses for tracing evolutionary patterns of parental rDNA in allopolyploid species were performed using the neighbor‐joining method. The D genome involved tree included three clades (CC‐DDCC, DDMM‐DDMMSS‐DDMMUU, and MM‐MhMh‐DDNN), but did not include Ae. squarrosa(DD). It indicated that the rDNA of ancestral D genome had been somewhat differentiated in allopolyploids. The U genome involved tree showed that the allopolyploids and their common ancestor, Ae. urnbellulata, formed a clade, suggesting that rDNA in UUMM and UUSS genomes has been homogenizing toward that of ancestral U genome. The phylogenetic pattern of U genome based on ITS sequences also supported the “pivotal‐differential” hypothesis.

The nucleotide sequences of the internal transcribed spacer (ITS) of nuclear ribosomal DNA in nine diploid species representing six sections of Aegilops were determined by direct sequencing of PCR-amplified DNA fragments. These sequences were aligned with two ITS sequences of additional species from Genbank. Sequence divergences were estimated using Kimura two-parameter model, and the phylogenetic analyses were performed using the maximum parsimony (MP) and the neighbor-joining (NJ) methods with PAUP and PHYLIP, respectively. The sequence divergences between the diploid species varied from 0.5% to 4.68%. The resulting MP tree and NJ tree showed relatively congruent phylogenetic relationships among these species, except Ae. caudata. Particularly, Ae. speltoides was basal within the two trees. The paraphyletic relationships between Ae. speltoides and two species of Sect. Sitopsis, and between Ae. uniaristata and two species of Sect. Comopyrum were supported strongly. The ITS data suggest that currently recognized sections within Aegilops should be reconsidered.