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Genomics and Applied Biology, 2011, Vol.2 No.6
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guaranteeing the existence of restorer genes only by
using the naked eye to determine the fertile phenotype.
It does not only smartly apply the theory of classic
three-line hybrid system, but also does not affect the
substitution of the nucleus background; (3) On the
premise of guaranteeing the existence of restore gene,
it has a larger choice to choose offspring plants that
are consistent with other phenotypic characteristics
and the genetic background of donor, which would be
more effective to substitute the genetic background; (4)
The method developed in this study might be a
relatively unique method for restorer breeding in
three-lines hybrid breeding of rapeseed, which should
be not only to reduce the workload for breeding
restorer lines, but the targeted candidate of restore
lines can reach 100% of recovery rate.
2.2 Comparison of detection methods for NIL’s
allelism
The near-isogenic lines obtained by using successive
backcross method might be failure because in the
course of backcrossing in different years individual
plant selection was influenced by the size of offspring
population, cultivating methods, trait properties and
other factors. Therefore, the allelism of candidate
must be assessed. Traditional detection methods for
allelism are generally to comparative agronomic traits,
which would be working well for these visible traits.
With the development of molecular biology, molecular
markers have been adopted by more and more
growing scholars. In this study, besides the use of
sterile cytoplasm to tag the existence of the restoration
genes, detecting the genetic background by using
molecular markers and combined with agronomic
phenotyping can identify much more excellent NILs,
that is the procedure for NIL’s background detection
by using both phenotype and genotype.
In this research we found that there is a certain
difference in the lines selected by approach of
phenotypic and genotypic selection. Phenotype is a
kind of the external appearance of internal genotype of
a line, which easily influenced by external environmental
conditions during its growth and development. Whereas
molecular detections mainly focus on identification of
genetic alleles and loci, statistically speaking, which is
a kind of sampling detection method that missing
detection occurs. It is impossible to have all loci
detected, so both of detection methods have some
shortages. This study attempts to use two methods to
evaluate the lines and mutually validate the data.
Although the best targeted lines selected by two
detection methods had some differences, the targeted
lines were those lines identified by both approaches.
Actually the results were similar. Finally, using two
detection methods can validate the results from single
detection to produce the better data. Definitely,
selecting excellent Near-isogenic lines would be very
important to fine mapping and gene cloning.
SSR, also known as microsatellite markers, presents a
kind of variability based on the length of repeat
nucleotide in the different locations of the living
genome (Von Diethard, 1989). Since the SSR came
out, with its stable reproducible and clear banding etc.,
SSR would be the dominant marker to tag the crop
traits in rice, cotton and other major crops (Zhang,
2009; Wang, 2005). In recent years, there have been
more distinctive types of molecular markers such as
AFLP, SRAP and others (Vos et al., 1995; Li et al.,
2001), Both of AFLP and SRAP have a good fit to
detect the differences between the parents, but detecting
the allelism of the homozygous lines is not better than
that of SSR. AFLP procedures are much more complex
including enzyme digestion than the procedures of
SSR. The authors also tried to use the SRAP to detect
allelism, which usually results in affecting the validity
of scoring the data because of its random primer
matching sites, more PCR products or multi-sites, or
differences in the amount of amplification or less
stability. Therefore, using SSR to detect the NIL’s
allelism would occupy some good advantages.
2.3 Genetic similarity of restorer gene near-isogenic
lines
Rapeseed (
Brassica napus
), a typical cross-pollinated
crops, is allotetraploid with high homology between
sub-genomic A and C. So in the breeding practice, it is
very common that the stable line with several
generation bagged-selfing still possible separate the
different line with different phenotype of the original
inbred lines. According to backcross protocol, the
classical the background substitution rate should be
96.875% after five generations of backcrossing. In this