Molecular Plant Breeding 2015, Vol.6, No.21, 1
-
17
1
Research Article
Open
Access
Assessment of Wheat Variety Uniformity using SSR Markers
Wang L.X. , Pang B.SH., Liu L.H., Li H.B., Zhao C.P.
Beijing Engineering and Technique Research Center for Hybrid Wheat, Beijing Academy of Agricultural and Forestry Sciences, Beijing 100097, China
Rm 506, Bldg 1, #9 Shu Guang huayuan Zhong Lu, Haidian District, Beijing 100097, China
Corresponding
authors
email:
Second corresponding authors
email
Molecular
Plant
Breeding,
2015,
Vol.6,
No.21
doi:
10.5376/mpb.2015.06.0021
Received:
20
Jul.,
2015
Accepted:
22
Aug.,
2015
Published:
14
Sep.,
2015
Copyright
© 2015 Wang et al.,
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Preferred
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for
this
article:
Wang L.X., Pang B.SH., Liu L.H., Li H.B. and Zhao C.P., 2015, Assessment of Wheat Variety Uniformity using SSR Markers, Molecular
Plant Breeding,
6(15)
1
-
21 (doi:
Abstract
Assessment of uniformity is important for wheat (
Triticum aestivum
L.) variety registration and protection. However, the
current testing system, which assesses a range of morphological characters, is time consuming (8-9 months for winter wheat), often is
altered by environmental factors, and is not suitable for the assessment of hundreds of samples. The objective of this study was to
develop a procedure for the assessment of wheat variety uniformity using simple sequence repeat (SSR) markers. Based on the
studies of the relationship between the homozygous loci ratio of SSR markers (SSR-HLR) and variety uniformity, and detection of
seed purity using SSR markers, we here propose that wheat variety uniformity is assessed on the basis of estimation of seed purity
and the SSR-HLR. A variety is uniform if its seed purity and SSR-HLR are both > 95%. A variety with an SSR-HLR < 91% and/or
seed purity ≤ 95% is not uniform. The varieties with an SSR-HLR ranging from 91% to 95% require additional uniformity
assessments in the field because not all of them are uniform or not uniform. Those varieties make up less than 10% of the varieties
(300-400) assessed in wheat regional trials annually in our laboratory, thus SSR markers are suitable for uniformity assessment of
~90% of wheat varieties. The procedures for uniformity assessment based on seed purity and SSR-HLR are detailed here. On average,
it takes only seven days to assess one variety following the proposed procedure and greatly shortens the assessment cycle. SSR
markers are not altered by environmental factors. Therefore, rapid and accurate assessment of a large batch of varieties becomes
possible.
Keywords
Wheat variety; Uniformity; SSR markers; Homozygous loci ratio of SSR markers
Introduction
The assessment of distinctness, uniformity, and stability
(DUS) in wheat varieties is a statutory requirement
before new varieties are registered and plant breeders'
rights are granted in China as a member country of the
International Union for the Protection of New Varieties
of Plants. Uniformity assessment of a wheat variety
involves evaluating whether there are significant
differences in phenotypic and agronomic traits among
individuals of a variety. The variety is considered
uniform if the number of off-type individuals does not
exceed a threshold value. On the basis of the national
standard
GB/T 19557.2-2004 entitled
Guidelines for
the conduct of tests for distinctness, uniformity and
stability-Wheat
(
Triticum aestivum
L.), issued in 2004,
uniformity assessment requires the testing of 56 traits
of at least 2000 plants of a variety over the course of
one cropping season (8-9 months for winter wheat),
and the variety is considered uniform if off-type plants
comprise less than 2.5%. This method has several
disadvantages, such as a long assessment period,
phenotype-environment interactions, and the difficulty
of distinguishing similar individuals. Therefore, rapid
and accurate assessment of a large batch of varieties is
impossible.
For development of a new assessment method, the
feasibility of molecular markers for testing variety
uniformity has been reported in corn, wheat, sugar
beet, tomato, and rape (De Riek et al., 2001; Cooke et
al., 2003; Wang et al., 2007; Lu et al., 2008; Wang et
al., 2009b). However, most authors confuse the
genotype of contaminant plants and non-homozygous
loci of the variety tested. This is bound to affect the
accuracy of uniformity assessments. We consider that
wheat variety uniformity assessment depends on both
the seed purity and homozygous loci ratio (HLR). The
analysis of individual genotypes using SSR markers
helps in detecting seed purity and SSR-HLR. If the
seed purity and/or SSR-HLR are lower than the
threshold values, the variety is not deemed to be
