Molecular Plant Breeding 2016, Vol.7, No.14, 1
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species was most likely to be the A sub-genome progenitor donor of allotetraploid cotton (AD)
1
and (AD)
2
.
The A
1-a
genome had been divided into the variant of A
1
genome in the taxonomy(Stewart, 1987). Many
researches always used the varieties of A
1
and A
2
genome species to study the origination and evolution of the A
sub-genome of allotetraploid cottons, but they seldom and nearly didn’t use the A
1-a
genome as the research
materials, and even some researchers took the A
1-a
and A
1
genome to lump together (Stewart, 1987; Wendel,1989;
Wendel and Albert, 1992; Wendel et al.,1994, 1995; Wendel and Wessler,2000; Wendel and Cronn,2002;Wang et
al., 2004). In this experiment, when using A
1-a
gDNA as probe we found that the GISH result was obviously
distinguished from the A
1
gDNA probe, and Wang et al(1995) had also found the karyotype parameters exist
significant differences between A
1
and A
1-a
genome. The A
1-a
genome made a strong independence from A
1
genome, and we suggested that A
1-a
genome should be given the “species” level in the classification of
gossypium
,
that’s means the A
1-a
genome possessed the same status with A
1
and A
2
genome.
2.2 The D sub-genome progenitor of (AD)
1
and (AD)
2
Since the discovery that allopolyploid
Gossypium
species contain two genomes whose progenitors presently occur
in different hemispheres, investigators had attempted to provide pieces to the puzzle of the polyploid origin. A
diverse array of tools had been used in an effort to examine this issue, from early study methods by comparative
morphology, cytology, cytogenetic, comparative phytochemistry, and protein electrophoretic methods to modern
phylogenetic investigations using DNA sequencing of homologous genes. Several investigators proposed that
allopolyploid cottons formed more than once, they suggested the best models of the potential D subgenome
ancestral donor of allopolyploid cottons were D
1
(
G. thurberii
), D
3-d
(
G. davidsonii
), D
3-k
(
G. klotzschianum
) and
D
5
(
G. raimondii
), so they considered the allopolyploid cottons are polyphyletic (Kammacher, 1960; Sherwin,
1970; Johnson, 1975; Umbeck, 1985; Stewart, 1987; Da and Bertrand,1995). However, Most authors proposed
that allopolyploid cottons formed only once, and that D
5
was more similar to the D subgenome of allotetraploid
cottons than other D genome diploids, they considered the allopolyploid cottons are monophyletic (Phillips,1963,
1964, 1966; Endrizzi et al., 1985; Wendel, 1989; Cronn et al.,1996; Seelanan et al., 1997; Small and Wendel,
1999, 2000; Wendel and Albert et al., 1992 ;Wendel et al., 1995; Wendel and Cronn, 2002; Admas, 2003).
We compared the GISH signals and DA values of (AD)
1
and (AD)
2
chromosomes generated by different diploid D
genome species. The DA values of D
6
(
G. gossypioides
) were much higher than those of other D genome species
both in (AD)
1
and (AD)
2
, but the signals were distributed on both A and D subgenome chromosomes of (AD)
1
and
(AD)
2
, and the signal intensity was much weaker than that produced by other D genome species such as D
3-d
(
G.
davidsonii
) and D
4
(
G. aridum
) in (AD)
1
, or D
1
(
G. thurberi
), D
3-d
(
G. davidsonii
) and
G. raimondii
(D
5
) in (AD)
2
.
Therefore, the D
6
genome species cannot be the D subgenome progenitor donor of (AD)
1
and (AD)
2
.
The signal intensity in D
3-d
probe was more stronger than any other D genome species probes in GISH of (AD)
1
,
and the DA value of
D
3-d
probe
was much higher than other D genome species too. This indicated that D
3-d
genome species has the strongest ability to recognize the D subgenome chromosomes of (AD)
1
, so we suggested
that D
3-d
but not D
5
was the possible D subgenome progenitor donor of (AD)
1
.
And on the other hand, the signal intensity in D
5
probe was more stronger than any other D genome probes in
GISH of (AD)
2
, and the DA value of D
5
probe was also much higher than other D genome probes.This indicated
that D
5
genome species has the strongest ability to recognize the D subgenome chromosomes of (AD)
2
, so we
thought that the D
5
is the possible D subgenome progenitor donor of (AD)
2
.
Previous GISH studies had shown that diploid D
1
and
D
3-d
genome species was the D sub-genome progenitor
donor of (AD)
4
(
G. mustelinum
) and
(AD)
5
(
G. darwinii
) respectively (Wu et al., 2010; 2013), combined with the
results of this experiment, allopolyploid cottons maybe formed with different D genome species as the progenitor
donor, these results supported the hypothesis that allopolyploid cottons are polyphyletic.
