Agriculture Reference
In-Depth Information
and the Middle East in 1989. The RWA from
Syria and Kirghiz regions were shown to severely
damage wheat with the
Dn4
gene (Puterka et al.,
1992). In 2003, a new biotype of RWA appeared
in Colorado which seriously damaged wheat that
carried the
Dn4
gene. This biotype, designated
RWA2, could acutely damage wheat with any one
of eight of the nine
Dn
resistance genes, with the
exception of
Dn7
(Haley et al., 2004). Biotypes
RWA3, RWA4, and RWA5 were soon discovered
which differentially damaged
Dn1
to
Dn9
resis-
tance in wheat (Burd et al., 2006). By 2005, RWA2
had already dominated the biotype complex in the
western US (Puterka et al., 2007). The extensive
distribution and predominance of RWA2 indi-
cated that wheat cultivars containing the
Dn4
gene would have little value in managing RWA.
Fortunately, the primary sources of RWA1 resis-
tance in barley, STARS 9301B and STARS
9577B, have remained resistant to all known RWA
biotypes (Puterka et al., 2006). Table 9.3 sum-
marizes the reactions of all sources of resistance
in wheat to Russian wheat aphid biotypes.
The origin of these new biotypes critically
remains undetermined. Wheat breeders in the US
are currently focusing efforts to move
Dn7
resis-
tance into wheat and fi nd new sources of resis-
tance to these biotypes. The threat of new RWA
biotypes to wheat production is not limited to the
US but also has become a problem in South Africa
(Tolmay et al., 2007). Effective deployment of
RWA resistance in cereals will rest on a thorough
characterization of biotypic diversity and testing
of candidate resistance genes in the fi eld, as well
as vigilantly monitoring RWA biotype frequency
after resistance gene deployment.
FUTURE PERSPECTIVES
Advances in controlling insect pests of wheat will
be dependent on research, development, and
deployment of new and better components of the
integrated pest management tactic. Better moni-
toring, understanding, and forecasting of insect
pest population buildup and movement is needed
to design and proactively implement IPM mea-
sures. New natural enemies for biological control
and new genetic sources of resistance in wheat
are needed that are effective, economical, and
durable.
The recent discovery of the chemical structure
of the sex pheromone produced by the adult
female Hessian fl y may lead to inexpensive and
convenient methods for monitoring Hessian fl y
populations. Artifi cial sex pheromone lures
deployed in sticky traps would catch adult males
and should provide much-needed information on
population dynamics, phenology, and geographic
distribution.
Research is needed to improve understanding
of the dynamics of fungal entomopathogens and
ways of manipulating fi eld conditions to favor
epizootics, including perhaps the use of mycoin-
secticides. Also, different natural enemy guilds
interact, and their interactions may affect net sup-
pression of insect pests. Evaluation of these inter-
actions is largely unexplored, and future studies
involving specifi c pests and particular combina-
tions of natural enemies are needed.
Potentially, the area where additional research
and development would have the most dramatic
positive impact on insect pest control is through
the introduction of new resistance genes to wheat
and the combination of multiple resistance genes
for deployment in a single cultivar. Resistance
genes currently used in available cultivars have
come from within the wheat genome or from
Table 9.3
Russian wheat aphid resistance genes and biotype
interactions in wheat.
Russian Wheat Aphid Biotype
Resistance
Gene
RWA1
RWA2
RWA3
RWA4
RWA5
Reaction to biotype
a
Dn1
S
S
S
S
S
Dn2
R
S
S
S
S
dn3
R
S
S
S
S
Dn4
R
S
S
R
R
Dn5
R
S
S
S
R
Dn6
R
S
S
R
R
Dn7
R
R
S
S
R
Dn8
S
S
S
S
S
Dn9
S
S
S
S
S
a
R and S indicate resistant and susceptible reactions,
respectively.
