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Molecular Plant Breeding 2011, Vol.2, No.07, 41
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47
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45
chinensis
, the results of AMOVA was coincidence
with another research results done by SSR in which
variation was significant contribution by inter-variety
variance too (Yim et al., 2009). In other words, factors
such as geography may have little effect on genetic
variation within varieties. The reason may be raised
that systematic breeding is a conventional and major
approaches for the development of new Caixin variety,
while recurrent selection within Caixin is inevitable to
bring about close genetic relationship and high
homogenizations in breeding program. Anyway, the
conclusion of low genetic diversity and close genetic
relationship within Caixin by AFLP analysis was
consistent with that by RAPD and ISSR (Tan et al.,
2009; Sun et al., 2010).
GD and GS are important indexes to evaluate the
relationship among varieties. The former indicates the
difference between varieties, the greater of the GD the
more difference existing between varieties. Whereas
the later is reverse, the greater of the GS the more
similar existing between varieties. In our work GD
ranged between 0.026 and 0.275 while GS ranged
between 0.76 and 0.943. Compared to results based on
RAPD (Tan et al., 2009) and ISSR (Sun et al., 2010),
as if there were more close relationship between
Caixin varieties and lines in this study. AFLP indeed
detect this kind of relationship. Cluster analysis
divided the 30 Caixins into four groups but cluster
pattern was still not very clear. It was same with the
researches mentioned above that Caixin varieties often
clustered together and isolated from other
Brassica
vegetables (Guo et al., 2002; Han et al., 2008; Ma,
2008; Tan et al., 2009; Sun et al., 2010). Although we
could find something interesting, for example, New
Zealand Si Jiu, Si Jiu
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19 and Caixingli Si Jiu grouped
together, the same way with Australia 608, Australia
008 dark green and Australia 50 Days. These results
testified that there must have very close relationship
between these varieties. The cluster results also
showed that the lines derived from some or other
parents grouped together. For instance, CX6
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6,
CX6
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6
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1, CX6
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7 and CX6
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13 grouped together in
the cluster I. These results implied that these varieties
or lines should have somewhat changes in genome
after long term artificial selection. Some lines such as
CX3
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1, CX3
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6 were not classified together, which
might imply that these germplasms have distinctly
genetic diversity.
In conclusion, AFLP is extremely useful and
efficiency and accuracy tool to assess genetic diversity
of Caixin varieties or lines, especially for lines which
have close relationship although it is considered that
the approach is high costs and time consumed and
complicated protocol. Compared with previous AFLP
analysis, our research work also revealed more
polymorphisms not only Caixin’s varieties but also
lines used in this study, therefore there were much
more information to be provided. In addition, the
genetic diversity of Caixin is very low and genetic
variations most attribute to varieties. It is without
question that molecular markers can enhance the
selection precision and breeding efficiency, but to
widen genetic fundament may need to be dependent
on new germplasm introduction. Therefore we strong
believe that novel breeding technologies such as
distant hybridization and transgenic technology should
be introduced into the Caixin breeding program in
order to solve the problem of narrow genetic
background.
3 Material and Methods
3.1 Plant materials
Thirty Caixins were employed in this study. These
varieties were collected from South China
(Guangdong province: Dong Guan 45 Days, Teqing
60 Days, Youqing no. 12, Si Jiu
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19, Mingyou 308
sweet, No. 31, Kuaida 28 Days, Youxin no. 2, Lv bao
701; and Guangxi province: Guiliu October, GX3
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1,
GX3
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6, GX3
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6
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1, GX5
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3, GX5
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4, GX5
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12,GX5
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14,
GX6
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6, GX6
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6
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1, GX6
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7, GX6
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13, GX6
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14,
GX9
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1, GX9
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4), Hong Kong (Hong Kong 45 Days,
Caixingli Si Jiu), Australia (Australia 008, Australia
608, Australia 50 Days) and New Zealand (New
Zealand Si Jiu).
3.2 DNA extraction
30 Caixin seeds were planted in the greenhouse.
Leaves of young seedling were randomly collected
from four individual plants each variety. Genomic
DNA was extracted from these mixed leaves by
modified CTAB method as follows. One gram of