Biology Reference
In-Depth Information
Table 7.1.
Races of the soybean cyst nematode
species
Heterodera glycines
, according to the race
determination scheme proposed by Riggs and Schmitt
(1988) (adapted from Niblack et al. 2006).
Table 7.2.
Indicator lines for HG Type classification
of genetically diverse populations of
Heterodera
glycines
nematode (Niblack et al. 2002).
Number
Indicator line
Number
Pickett
Peking
PI 88788
PI 90763
1
PI 548402 (Peking)
1
−
−
+
−
2
PI 88788
2
+
+
+
−
3
PI 90763
3
−
−
−
−
4
PI 437654
4
+
+
+
+
5
PI 209332
5
+
−
+
−
6
PI 89772
6
+
−
−
−
7
PI 548316 (Cloud)
7
−
−
+
+
8
−
−
−
+
9
+
+
−
−
10
+
−
−
+
according to a standard phenotyping protocol.
An SCN population is named according to the
number associated with the soybean indicator
lines (Table 7.2) on which it is virulent. SCN
virulence is measured as female index (FI, %)
as described in the race determination system
above. HG Type of an SCN population is then
reported by numbers separated by periods. For
example, the HG Type of a SCN field population
is described as 2.5.7, meaning this SCN popula-
tion is virulent on three indicator lines, PI 88788
(2), PI 209332 (5), and PI 548316 (7), with FI
values greater than 10%. Recently, the HG Types
classification scheme has been commonly used
in various genetic studies of SCN (Afzal et al.
2012; Arelli et al. 2009; Vuong et al. 2010, 2011;
Wu et al. 2009).
11
−
+
+
−
12
−
+
−
+
13
−
+
−
−
14
+
+
−
+
15
+
−
+
+
16
−
+
+
+
differential was counted and used to estimate
female percentage (%), based on the number of
females produced on the standard check cultivar
Lee. Later, Riggs and Schmitt (1988) expanded
the original scheme to a logical characterization
of a new race designation by adding 16 new SCN
races. For many years, this new system has been
widely adapted by public and private soybean
scientists to characterize
H. glycines
populations
and resistance genes in soybean lines (Table 7.1).
However, due to incorrect characterization of
SCN populations resulting in misinformation to
soybean growers, a new classification and desig-
nation system was proposed (Niblack et al. 2002)
that uses several sources of resistance as indica-
tor lines (Table 7.2) to characterize and expand
the genetic diversity of SCN. The term “HG
Type” that stands for
Heterodera glycines
was
adapted in place of “race” to classify SCN pop-
ulations. This scheme is open-ended, meaning
additional soybean indicators can be added, and
it is easily adaptable to different geographical
areas (Niblack et al. 2002).
In order to classify the HG Type of a
H.
glycines
population, a bioassay is conducted
SourcesofResistancetoSCNandQTL
Mapping
Planting cultivars resistant to SCN and rotating
soybean with non-host crops have demonstrated
to be effective and practical measures for
controlling SCN infestation that causes severe
yield losses in soybean. For decades, soybean
scientists in both public and private sectors have
successfully developed several SCN-resistant
cultivars, allowing the continuation of soybean
production in large growing areas where soy-
bean production could no longer be profitable
due to SCN infestation (Concibido et al. 2004).
For example, it was reported that the soybean
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