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QTL mapping is based on the phenotypic values of
quantitative traits which can be the interaction results
of genotype and environment, so there were probably
errors in QTL analysis when using phenotypic values,
i.e., the effect of QTLs could be significantly
influenced by environment (Tinker et al., 1996). For
instance, 29 QTL were detected in tomato that grew up
in the three environments, but only four QTLs have
significant expression in the three environments
(Paterson et al., 1991). However, some studies
suggested the environment had little effect on major
QTL and was stable in different environments
(Tanksley et al., 1982; Hayes et al., 1993). Therefore,
the collection of phenotypic value for QTL mapping
should exclude the error caused by the environment as
much as possible so that those values could truly show
the characteristics and differences of the traits. On the
other hand, major QTL should be selected as possible
as the genes or sequences conferring the traits would be
tracked and cloned.
It is very difficult to develop the genetic linkage maps
and do QTL analysis for
Phalaenopsis
due to its
complicate genetic background of the heterozygosis and
numerous chromosomes. QTL analysis for
Phalaenopsis
based on molecular linkage groups would possibly be
another useful and convenient way for finding out the
gene sequences associated with quantitative traits. With
the construction of higher density molecular genetic
maps using different molecular markers, more
quantitative traits loci will be located and the accuracy of
positioning will be improved, which would be helpful for
cloning of genes and molecular marker-assisted breeding
for
Phalaenopsis
in the future.
3 Materials and Methods
3.1 Plant materials
The materials for AFLP and QTLs analysis from a
hybrid population
Phal.20
x
Phal.462
are developed
by Guangdong Academy of Agricultural Sciences.
Phal.462
has creamy white flowers overlaid with big
waxy magenta spots, big leaf, and non-flavor;
Phal.20
has creamy yellow flowers with small mahogany spots,
middle leaf, and weak flavor. 88 progenies were
randomly selected from 450 hybrid population for
QTL analysis.
3.2 Collection of leaf traits and AFLP molecular
linkage mapping
According to UPOV (2003) new varieties of
Phalaenopsis
DUS testing guidelines, the leaf length (leaf length, LL)
and leaf width (leaf width, LW) were measured. At the
flowering stage, choose the longest leaf. Plant size was
represented using plant width (plant width, PW), which
was the maximum length between two leaves. The
molecular genetic maps of
Phalaenopsis
were
constructed according to CP models using Joinmap3.0
software (Xu, 2010).
3.3 Data statistic and QTL analysis
Data of the traits were analyzed using SPSS13.0.
The
phenotypic effect of individual QTLs was estimated by
MapQTL5.0 (Van et al., 2004). The genetic linkage map
was described by interval mapping (IM) (Lander and
Botstein, 1989). This stringent threshold, similar to an
LOD score of 3.0, is used to achieve an experiment-wise
false positive rate no higher than 0.05. The percentage of
phenotypic variance explained by each QTL and the
percentage of phenotypic variance explained by the
QTLs given all the covariants were also estimated by
Win QTL Cartographer. QTL nomenclature follows a
method used in rice (McCouch et al., 1997), starting with
‘q’, followed by an abbreviation of the trait name [
leaf
length (LL), leaf width (LW), plant width (PW)
] and
the name of chromosome, then followed by a number.
Authors
'
Contributions
SPX, XRL, and JML executed this study; SPX completed the
data analysis and wrote the first draft; XRL, and JML involved
in experimental design and analysis of the results; GPW
directed the molecular marker technology and data processing;
FQL was the instructor who involved in guiding the study and
essay writing and modify. FXL was the planner and responsible
person of this study, who developed the hybrid population,
directed the experimental design, data analysis and thesis
writing. All authors have read and approved the final
manuscript.
Acknowledgements
This paper was funded by the Programs (2008A020100019)
and (2005B20901001) of Guangdong provincial Science and
Technology Department. Much thanks to Mr.Zhang Mongjin
and Ms Cai Shaohui who helped to develop the hybrid
population.
References
Been C.G., Na A.S., Kim J.B., Kim H.Y., 2002, Random amplified
polymorphic DNA (RAPD) for genetic analysis of Phalaenopsis species,
Journal of the Korean Society for Horticultural Science, 43(4): 387-391