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Discussion
As described above, T. aestivum var. spelta differs
from the four special Chinese hexaploid wheat landraces by one to two
pairs of chromosomes, and the D genome in these four Chinese
landraces were more primitive than the D genome of T. aestivum
var. spelta. These results reveal that the four special
Chinese hexaploid wheat landraces may originate independently and
later than this T. aestivum var. spelta.
Based on the results of this study, the four special Chinese
landraces may be classified into two groups. The first group is
composed of TW, YH and SW (which is represented by CS). Members in
this group have similar genomes. Riley et al (1967) discovered that
the A, B and D genomes of CS were structurally unchanged relative to
A and B genomes of T. turgidum var. dicoccoides and the
D genome of Ae. tauschii Cosson respectively. The present
study showed that the A, B and D genomes in TW, YH and SW were as
primitive as those of CS. Therefore, they might be derived from the
same progenitor and thus may be grouped together and called "Chinese
Spring group". In this group, TW has some wild, primitive characters
such as fragile spike, and its D genome is closer to the D genome of
Ae. tauschii Cosson than the D genomes of other members.
Therefore, TW might originate from cross between T. turgidum
and Ae. tauschii at the middle portion of the Yellow River
Valley and thus be the progenitor of this group. It is possible that
the ancestor hybrid derivatives were later introduced into Sichuan,
Yunnan and Tibetan area and envolved into YH and SW through natural
and human selection.
Xinjiang Rice Wheat composes the second group. The present study
showed that XR differs from the CS group by two pairs of chromosomes.
Our observation also indicated that one of the two chromosomes may be
chromosome 6B. In their analysis of XR with CS ditelosomics, Chen et
al (1988) pointed out that it was the B genome that differed between
these two landraces. It seems that it is not the D genome chromosome,
as suggested by Yao et al (1983), but the B genome chromosomes that
differ between these two landraces. XR also differs from SP by two
chromosomes. Chen et al (1988) reported that there was little
difference between the D genomes of XR, TW, YH and CS. It might
indicate that the D genome of XR may also be primitive. The present
study reconfirmed the results of Riley et al (1967) that SP differed
from Ae. tauschii by one pair of D genome chromosome. The
present study also showed that XR differs from SP by one to two pairs
of chromosomes. Therefore, XR might not originate from a hybrid
between T. turgidum L. var. polonicum and the Chinese
Spring group nor evolve from T. aestivum var. spelta as
suggested by Chen (1985). Instead, XR might be derived from a hybrid
between Ae. tauschii and an emmer wheat in which the B genome
had changed. From the viewpoint of morphology, this emmer wheat may
be T. turgidum L. var. polonicum.
Acknowledgements
The authors thank very much Dr. Yang Yen for his careful reading and
helpful assistance in the preparation of the manuscript.
References
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