Agriculture Reference
In-Depth Information
The Hessian fl y is somewhat unusual as an
insect pest in that insecticides are rarely used
(Berzonsky et al., 2003). Reasons for this include
the availability of highly effective noninsecticidal
methods, the diffi culty of monitoring Hessian fl y
populations, and the unpredictable, localized,
and/or sporadic nature of outbreaks. Noninsecti-
cidal methods include host-plant resistance,
planting after the “fl y-free date,” and removal of
hosts that provide a “green bridge” between the
harvest of one crop and the planting of the next.
Planting after the fl y-free date relies on tempera-
ture models that predict the last possible date
during autumn when adult females are present in
fi elds. Winter wheat crops planted after this date
escape egg laying and subsequent larval attack
during the vulnerable seedling stage. In areas with
mild winters, this method is not used because
adult emergence, female egg laying, and larval
attack can occur during short periods of warmer
weather. The effectiveness of removing bridging
hosts such as volunteer wheat depends on whether
there are other grasses in the area that can serve
as hosts.
press the outbreak that threatened wheat, which
was one of the new Republic's most important
exports (Hunter 2001). Since that time, over 30
genes effective against the Hessian fl y have been
designated H1 through H32 . Table 9.1 shows the
reactions of major sources of resistance in wheat
to several biotypes (Ratcliffe and Hatchett
1997).
These genes have been found in both wild and
domesticated grasses. Most commonly, this resis-
tance is conditioned by dominant alleles at major
resistance loci. Resistance has a dramatic effect
(Berzonsky et al., 2003; Harris et al., 2003). Host
acceptance of the adult female and neonate larva
remains the same, but the larva dies soon after
attack. The resistant seedling shows only minor
growth disturbances (Anderson and Harris
2006).
Resistance to the Hessian fl y can be compro-
mised by the development of parasite virulence
via modifi cations in matching avirulence ( Avr )
genes (Stuart et al., 2007). For example, three
resistance ( R ) genes, H3 , H5 , and H6 , were over-
come by virulent biotypes after 15, 9, and 22
years, respectively (Foster et al., 1991). Starting
with Gallun (1977), classical Mendelian genetic
principles have been used to investigate the rela-
tionship between H genes and corresponding
Hessian fl y Avr genes (Stuart et al., 2007). The
genetics of the interaction fi t the gene-for-gene
model initially developed by Flor (1946). This
type of gene-for-gene interaction appears to be
unique to Hessian fl y-wheat and is considered
Utilization of host-plant resistance
In North America, the use of host-plant resis-
tance has a long history of success (Berzonsky et
al., 2003; Harris et al., 2003). Indeed, within 10
years of the discovery of Hessian fl y populations
on Long Island in 1777, a highly effective plant
resistance trait was discovered and used to sup-
Table 9.1 Hessian fl y resistance genes and biotype interactions in wheat.
Hessian Fly Biotype
Wheat Genotype & H gene
Origin of H gene
GP
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
Reaction to biotype a
Caldwel
H3
T. aestivum
RRSRSSRSRRSRSSRS
Magnum
H5
T. aestivum
RRRRRRRRSSSSSSSS
Monon
H6
T. turgidum
RRRSSRSSRRRSSRSS
Seneca
H7H8
T. aestivum
RSSSSRRRRSSSSRRR
a R and S indicate resistant and susceptible reactions, respectively.
 
Search WWH ::




Custom Search