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Genomics and Applied Biology, 2011, Vol.2 No.6
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et al., 2006).
In the building process of near-isogenic lines, generally,
each generation used to be done by phenotypic
selection. After multi-generation crossing, there is
little interaction between traits and environments,
some negative factors such as the linkages of the
donor gene fragments with target genes can make the
bias to select the offspring lines, which will affect the
quality of building the near-isogenic lines. Thus, after
the near-isogenic lines built, it is very necessary to
assess the allelism of the candidates of near-isogenic
lines. In the early, traditional methods commonly
phenotypic trait or traits related to the studied objects
were used to evaluate the near-isogenic lines, whereas
the molecular markers rapidly developed in recent
years have been used for detecting the allelism (Shen,
2004; Ma, et al., 2007; Liu, 2006; Liu, et al., 2008; Xu,
et al., 2008).
The near-isogenic lines of the restore genes in MI
CMS rapeseed hybrid system is a powerful tool for
tagging and cloning the restore genes. Since 2002 the
authors had started to build the near-isogenic lines of
restore genes of MI CMS system, we obtained the
near-isogenic lines with three different genetic
backgrounds through crossing with three genetic
background elite germplasms and selecting in the
multi-generation backcross. Although there are lots of
approaches for the near-isogenic lines, it is almost
blank using multiple methods to simultaneously detect
the allelism. In this study we carried out the genetic
similarity of some candidates of near-isogenic lines of
restore genes derived from three different genetic
backgrounds by using rapeseed (
AACC
) SSR, and
assessed the allelism of candidates to their donor’s
background by combining agronomic trait analysis of
candidate lines. We attempted to obtain the best
near-isogenic lines of restore genes to lay a solid
foundation for tagging and cloning the restore genes
in MI CMS system.
1 Results and Analysis
1.1 Building the near-isogenic lines of the fertile
restoring genes in MI CMS
In this research we employed Ning R7 as the source of
restoring gene, T78, T84 and ZS9 as the donors of
genetic backgrounds. Since 2002, we adopted the
continuous backcrossing procedures method to
substitute the genetic background to select far more
similar individuals with donor’s phenotypes for further
backcross. Up to 2008, we reached BC
5
F
1
generation
with three different genetic backgrounds. In the
beginning of the BC
5
F
1
generation, we adopted the
strategy by combining the backcrossing and selfing to
continually increase the substitution rate of the genetic
background. In the generations of BC
6
F
1
and BC
5
F
2
generations, fertility segregation was investigated in
the flowering stage to eliminate the lines that had
fertility segregating. In BC
5
F
3
generations, lines with
full fertile individuals were selected to be as tentative
candidates of near-isogenic lines with homozygous
restore genes. In 2010, seven, six and eight candidate
NILs related to three genetic backgrounds respectively
were come out (Table 1). The detailed building
procedures were shown in Figure 1.
Figure 1 The building route of the NILs for restorer genes
Note: ZZ stands for three genetic background donor germplasms
1.2 Phenotyping agronomic traits of NIL candidates
The variance analysis of agronomic traits among the
NIL candidates and three genetic background donors
was carried out by using t-test (Table 1). The results
showed that the lines being differences in agronomic
traits but having a higher genetic similarity with the