Molecular Plant Breeding 2015, Vol.6, No.21, 1
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Table 1. Given that the non-homozygous SSR loci
result in different genotypes within a population of a
particular variety, 20 individuals of A2009-75 were
classified into 20 genotypes, which each differed from
other genotypes at 1-19 loci. The genetic similarity
coefficient (GS) of each pair of individuals with
different genotypes ranged from 0.85-0.99. In most
instances, a pair of varieties is phenotypically distinct
if their GS is 0.85-0.99 (Wang et al., 2010; Wang et
al., 2015). Therefore, most pairs of A2009-75 individuals
with different genotypes exhibited genetic distinctness.
The grains of the 20 individual plants of A2009-75 were
harvested in 2009, and grown by the plant-to- row
method in the field the following years (2009–2010).
Phenotypic and agronomic traits were compared among
20 rows following the Materials and Methods.
Significant difference of plant height, flag leaf length,
thousand-grain weight, and heading date among the rows
were obvious (Table 2). This indicates that the variety
was not attained uniformity and SSR-HLR could be an
index of wheat variety uniformity.
Relationship between the homozygous SSR loci
ratio and the uniformity of wheat varieties
To confirm the relationship between SSR-HLR and
uniformity or stability of wheat varieties, a set of
experiments were conducted in common because both
detection of SSR-HLR and phenotypic observation
provided the data for the two studies. In 2008, 2009
and 2010, the grains of 20 individual plants of 10-20
varieties with an SSR-HLR ≤ 95% in the regional
trials were harvested annually, and grown by the
plant-to-row method in the field the following years
(2008-2009, 2009-2010 and 2010-2011). Concurrently,
5-10 varieties with an SSR-HLR > 95% were grown
annually as a control. Phenotypic and agronomic traits
were compared among 20 rows of each variety. A
significant difference among the rows of a variety,
according to the criteria described in Table 5, showed
that the variety was still segregating and had not
attained uniformity and stability. Among approximately
60 varieties, trait segregation was distinct in varieties
with an SSR-HLR < 91%, but seldom occurred in
varieties with an SSR-HLR > 95%. For a few of the
varieties with an SSR-HLR ranging from 91% to 95%,
the traits performed identically, but obvious segregation
was also observed in other varieties. This indicated
that the varieties with an SSR-HLR > 95% were
uniform and stable, but the varieties with an SSR-HLR <
91% were not. The varieties with an SSR-HLR
ranging from 91% to 95% required additional field
observation for uniformity and stability assessment.
The data listed in Table 3, which shared in an article
about stability assessment (Wang et al., 2014a) and
this article, shown the varieties not to be uniform and
stable in the 3 years.
Criteria for uniformity assessment of wheat varieties
using SSR markers
A variety is not uniform if it contains contaminant
plants and/or non-homozygous loci above threshold
values. The phenotype of a contaminant plant differs
from those of the majority of plants in a wheat variety.
In addition, a lower HLR also causes inter-plant
phenotypic differences in a wheat variety. On the basis
of the Chinese national standard (GB/T 19557.2-2004),
the variety is uniform if off-type plants are less than
Table 1 Number of individual with three genotypes at eight loci of 20 A2009-75 individuals
Genotype
Number of individuals with three genotypes
Xgwm261
Xcwm65
Xcfd76
Xwes26
Xgwm161
Xwmc764
Xswes185
Xksum73
aa
10
9
10
11
12
11
10
11
ab
2
2
0
0
1
1
1
0
bb
8
9
10
9
7
8
9
9
Table 2 Significant difference of four traits among 20 rows of A2009-75
Among 20 rows
Plant height (cm)
Flag
leaf length (cm)
Thousand-grain weight (g)
Heading date
Maximal value
63.8
21.4
48.2
Nine lines were on May 11
Minimum value
56.6
16.8
37.0
Six lines were on May 9
Range
7.2
4.6
11.2
Two days
