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(3) RFLP analysis of eight
common wheat and one emmer wheat accession (Liu et al 1990): Using
the unique sequences as probes, RFLPs among eight common wheats and
an emmer wheat were investigated. The proportion of the clones
revealed RFLPs among the eight common wheats was about 41% in the
unique sequences, whereas it was only 11% in the moderately repeated
sequences (ca.102-103 copies/haploid nucleus).
No highly repeated sequences exhibited RFLP among the eight common
wheats. In total, 271 probe-enzyme combinations were used, 71
combinations (27%) of which revealed RFLPs among the eight common
wheats. Based on the total number of hybrid bands observed in each
wheat, and the number of differential hybrid bands observed between
all wheat accessions, the genetic distances between them are
calculated after Nei (1987). The average distance between eight
common wheats was 0.71 x 10-2 (range, 0.38---0.935 x
10-2), whereas that between them and an emmer wheat was
2.06 x 10-2 (range, 1. 86 --- 2.44 x 10-2),
indicating great nuclear genome differentiation between emmer and
common wheats as compared to the differences among common wheats.
This is mainly due to the absence of the D genome in emmer wheat. The
eight common wheats were classified into three groups, (1) four Asian
wheats, (2) three Western wheats, and (3) Spelta. Tibetan semi-wild
wheat showed the closest relation to CS, supporting an idea that the
former is a recent derivative of the Chinese cultivated wheat
(Tsunewaki et al. 1990). Spelta greatly differed from all other
common wheats. This and the fact described in the previous section
are in favor of the origin of Spelta from the hybridization between
emmer and common wheat, as suggested by Schiemann (1951) and
Tsunewaki (1968).
(4) RFLP analyses of wild tetraploid wheats, einkorn wheat and Ae.
squarrosa : RFLPs between large numbers of T.
dicoccoides and T. araraticum accessions, together with
a limited numbers of T. durum, T. timopheevi
and T. aestivum, have been carried out by Mori et al
(1991). Their results demonstrated that the nuclear genomes of emmer
and timopheevi groups of wheat have been greatly differentiated from
each other, with no intermediate types, indicating the diphyletic
origin of these two tetraploid wheat groups. RFLP analysis of einkorn
wheat was carried out by Takumi et al (1991), using seven accessions
of T. boeoticum, T. urartu and T.
monococcum,with a single accession each of emmer and common
wheat as referants. In total, 88 probe-enzyme combinations were
employed. The results clearly indicated that T. monococcum was
derived from T. boeoticum, whereas the A genome of
emmer and common wheats was originated from T. urartu, fully
supporting the results of Dvorak (1988) which were obtained with the
repeated sequence clones as probes. RFLP analysis of five Ae.
squarrosa accessions collected from different locations, with a
common wheat as a referant, was carried out by Achiwa (1990), using
81 probe-enzyme combinations. In this case, 27 unique sequence clones
of the genomic DNA of Ae. squarrosa were used as probes. The
accessions collected from the same regions had similar nuclear
genomes even though they belonged to different taxonomic varieties,
whereas those of the same variety from different regions showed
differentiation of their genomes. The nuclear genomes of Ae.
squarrosa accessions collected from south to west coastal regions
of Caspian Sea showed close relation to that of common wheat,
supporting the proposal of several workers (Tsunewaki 1968, and
others) that this region is the birthplace of common wheat.
(5) Structure of a hypervariable sequence, TAG 546, and its use in
common wheat cultivar identification (Liu and Tsunewaki 1990, Liu et
al 1991): A hypervariable sequence was found among the genomic DNA
clones of CS, and was designated TAG546. When this clone was used as
probe, single enzyme digests of the nuclear DNAs of eight common
wheats (ref. section (2)) could be distinctly discriminated from each
other. Encouraged by this finding, the nuclear DNAs of 56 common
wheat cultivars collected from various countries, some of which are
very closely related to each other in their pedigrees, were treated
with three 6-base cutters, and their fingerprints probed with TAG546
were compared. All the cultivars could be successfully identified by
this fingerprinting.
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