Agriculture Reference
In-Depth Information
High-temperature adult-plant resistance
same genotype. Data from fi eld plots sometimes
indicate the presence of HTAP resistance, espe-
cially in areas where stripe rust infection occurs
in the seedling stage. However, a mixture of avir-
ulent and virulent races to specifi c Yr genes can
confound these results. Expression of HTAP
resistance can be infl uenced by temperature, by
growth stage at which infections fi rst occur, and
by the amount of inoculum. Infection type and
disease severity are most commonly used to
measure HTAP resistance. Infection types are
relatively stable, but can be affected by tempera-
ture and plant growth stage. Severity levels of
cultivars with HTAP resistance tend to vary
across regions and years due to differing levels of
rust inoculum and temperatures.
The genetics of HTAP resistance has been
studied in numerous wheat cultivars. Segregation
for stripe rust resistance in adult plants differed
from segregation in seedling plants, which indi-
cated that different genes control resistance in
different growth stages (Allan et al., 1966). Milus
and Line (1986a) determined that Gaines had one
gene and Nugaines and Luke had two genes for
HTAP resistance. Gaines and Nugaines had a
gene in common, but the HTAP genes in Luke
were different. Chen and Line (1995a,b) deter-
mined two to three genes or QTLs conferred
HTAP resistance in 'Druchamp' and Stephens.
The cultivars differed for HTAP resistance genes
and for race-specifi c resistance genes. In these
studies, HTAP resistance genes in all cultivars
were partially recessive and there was an additive
effect when two or more genes were present in a
genotype.
Several genes that condition adult-plant or
HTAP resistance have been reported (with their
known cultivar source): Yr11 ('Joss Cambier'),
Yr12 ('Frontier'), Yr13 ('Hustler'), Yr14
('Kador'), Yr16 ('Bersee'), Yr18 ('Jupateco 73R'),
Yr29 ('Pavon F76'), Yr30 ('Opata 85'), Yr34
('WAWHT2046'), Yr36 ('Glupro'), and Yr39
(Alpowa). In addition a large number of QTLs
that condition HTAP or adult plant stripe rust
resistance have been characterized (Worland and
Law 1986; Chen et al., 1998; Boukhatem et al.,
2002; Chen 2005; Santra et al., 2006; William et
al., 2006; Chen and Lin 2007; Chen and Zhao
In contrast to race-specifi c resistance, HTAP
resistance cannot be detected in seedling plants.
Cultivars with only HTAP resistance are highly
susceptible in the seedling stage. At higher tem-
peratures in older plants resistance is most appar-
ent, with more resistance expressed in fl ag leaves
than in lower leaves. The typical HTAP resis-
tance in the spring wheat cultivar Alpowa is
shown in Color Plate 10b. The HTAP resistance
was fi rst characterized by Line (1972) and further
described in later studies (Qayoum and Line
1985; Milus and Line 1986a,b; Chen and Line
1995a,b; Line and Chen 1995).
The HTAP resistance in Gaines and Nugaines
has remained effective for more than 40 years
under frequent stripe rust epidemic conditions.
Gaines and Nugaines were widely grown in the
Pacifi c Northwest until 1981 (Line 2002), when
new cultivars with higher levels of resistance were
developed. The cultivar Luke with a much higher
level of HTAP resistance than Gaines or Nugaines
was released in 1970. Currently, wheat cultivars
widely grown in the Pacifi c Northwest, such as
Stephens, 'Madsen', 'Eltan', and 'Rod' soft white
winter wheat, 'Bauermeister' hard red winter
wheat, and Alpowa, Express, and 'Louise' spring
wheat have HTAP resistance.
In the Great Plains, the widely grown cultivar
Jagger with HTAP resistance has reduced losses
to stripe rust in this region since 2000. Cultivars
with HTAP resistance have also reduced yield
losses compared with susceptible cultivars in
California and the south central states where
stripe rust develops in early growth stages (Uauy
et al., 2005). Cultivars with HTAP resistance can
affect the epidemiology of stripe rust, as stripe
rust infections on these cultivars produce fewer
urediniospores, thus reducing the overall level of
stripe rust inoculum. Increased use of cultivars
with HTAP resistance will decrease inoculum
levels and thus reduce yield losses over a wide
geographic area.
To identify wheat lines with HTAP resistance,
adult plants should be tested at defi ned high (10-
35 ºC) and low (4-20 ºC) temperatures with stripe
rust races that are virulent to seedlings of the
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