Molecular Plant Breeding 2016, Vol.7, No.14, 1
-
10
6
chromosomes of (AD)
2
, while the other 12 D gDNA show weaker ability to recognize the D sub-genome
chromosomes of (AD)
2
, so the D
5
genome species had closer genetic relationship with the D sub-genome of
(AD)
2
.
Table 2 DA values of all diploid A, D genome species probes generated by GISH of (AD)
1
and (AD)
2
probe
(AD)
1
(AD)
2
G. herbaceum
(A
1
)
0.361
0.343
G. arboreum
(A
2
)
0.358
0.346
G. herbaceum
wild speices
(A
1-a
)
0.369
0.352
G. thurberi
(D
1
)
0.258
0.247
G. armourianum
(D
2-1
)
0.136
0.189
G. harknessii
(D
2-2
)
0.102
0.111
G. klotzschianu
(D
3-k
)
0.087
0.071
G. davidsonii
(D
3-d
)
0.286
0.252
G. aridum
(D
4
)
0.274
0.241
G. raimondii
(D
5
)
0.255
0.263
G. gossypiodies
(D
6
)
0.402
0.387
G. lobatum
(D
7
)
0.081
0.044
G. trilobum
(D
8
)
0.096
0.076
G. laxum
(D
9
)
0.085
0.058
G. turneri
(D
10
)
0.083
0.065
G. schwendimanii
(D
11
)
0.231
0.098
2 Discussion
2.1 The A sub-genome progenitor of (AD)
1
and (AD)
2
Since the discovery that allotetraploid
Gossypium
genomes contain both A and D genomes, investigators had
attempted to look for which one of the modern diploid A and D genome species can be best served as the
progenitor genome donors of allopolyploid cottons.
Which one of the diploid A genome species was the really donor of the A sub-genome of allopolyploid cottons?
Many previous researches suggested that
G. herbaceum
(A
1
) was the donor or the similar ancestors of the
allopolyploid A sub-genome (Beasley, 1940; Gerstel, 1953; Phillips, 1963; 1964). However, the subsequent
research had shown that there existed much differences between
G. herbaceum
(A
1
) and the A sub-genome of
allopolyploid cotton, whether in the chromosome or molecular level (Wendel, 1989; Wendel and Albert, 1992
；
Cronn, et al., 1996). And cell cytogenetic and comparative mapping research also revealed that there existed at
least two large translocations between their genomes (Gerstel, 1953
；
Small, et al., 1998
；
Liu and Wendel, 2001).
Branch taxonomy analyses of the molecular sequences had showed that
G. herbaceum
(A
1
) was not the actual
progenitor of the A sub-genome of allotetraploid cottons (Endrizzi, et al., 1985; Wendel and Cronn, 2002). In the
evolutionary process of allotetraploid cottons,
G. herbaceum
(A
1
) and
G. arboretum
(A
2
) were the phylogenetically
sisters between each other and hence were genealogical equidistant to the A sub-genome of the allotetraploid
cottons (Cronn et al., 1996; Liu and Wendel, 2001; Wendel, 1989; Wendel and Albert, 1992).
In our experiment, GISH of (AD)
1
and (AD)
2
both with all 3 A genome gDNA as probes, 13 pairs of A
sub-genome chromosomes were painted with red fluorescence signals, and the DA value was very similar between
A
1
and A
2
gDNA probe, there was no significant difference between A
1
and A
2
both in GISH of (AD)
1
and (AD)
2
,
while the DA value of A
1-a
gDNA probe was higher than A
1
and A
2
gDNA probe, the A
1-a
gDNA had the strongest
ability to recognize the A sub-genome chromosomes of (AD)
1
and (AD)
2
, so we considered that A
1-a
genome
