Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

54
A Possible Gene-for-Gene Relationship for Septoria Tritici
Leaf Blotch Resistance in Wheat
P.A. Brading, 1 G.H.J. Kema, 2 and J.K.M. Brown 1
1 Cereals Research Department, John Innes Centre, Norwich, UK
2 DLO-Research Institute for Plant Protection (IPO-DLO), Wageningen, The Netherlands
Abstract
In an F2 population of a cross between the resistant variety Flame and the susceptible variety Longbow it was shown that
Flame carried one partially recessive gene for resistance to Septoria tritici isolate IPO323, as measured in a detached leaf
assay. Work is underway to determine whether this resistance gene has a gene-for-gene relationship with the single avirulence
locus identified in the IPO323 isolate.
Septoria tritici leaf blotch,
caused by the fungus
Mycosphaerella graminicola
(anamorph Septoria tritici), is one of
the most serious foliar pathogens of
wheat in Europe. In recent field
trials using individual M.
graminicola isolates, specific variety
x isolate interactions have been
observed (Kema and van Silfhout,
1997). A number of wheat varieties
show specific resistance to the
Dutch isolate IPO323, including the
British varieties Flame and
Hereward (Brown et al., 1999). In
Holland, crosses have been made
between IPO323 and another
isolate, IPO94269. Avirulence of
IPO323 on three specifically
resistant cultivars, Shafir, Kavkaz,
and Veranopolis, appears to be
controlled at a single locus with
simple inheritance (Kema et al.,
1999). To investigate whether the
specific resistances of Flame and
Hereward to IPO323 conform to a
gene-for-gene relationship and also
whether Flame and Hereward
share the same resistance gene,
crosses between Flame, Hereward,
and a susceptible variety, Longbow,
have been made.
Eighty F 2 seedlings from a cross
between Flame and Longbow were
tested in a detached leaf assay
(Arraiano et al., 1999) in which
primary and secondary leaves were
inoculated with IPO323. Leaf
sections were scored according to
the percentage leaf area covered
with lesions bearing pycnidia 15-28
days after inoculation. Each F 2
plant was represented by four leaf
sections tested in separate boxes.
The parental varieties, Flame and
Longbow, were also included in
each box. Comparison of infection
levels on all four replicate leaf
sections allowed individual plants
to be rated as resistant, susceptible
or intermediate. Flame was always
resistant and Longbow always
susceptible. Of the 80 progeny
tested 23 were scored as resistant
(less than 10% infection on all
leaves). The other 57 progeny were
scored as either susceptible (all leaf
sections heavily infected) or
intermediate (variable levels of
infection). The 1:3 ratio of
resistant:susceptible/intermediate
is consistent with a single, partially
recessive resistance gene in Flame.
F 3 families generated from the
80 F 2 individuals are being tested
as seedlings (GS 25) in a polytunnel
to test the prediction of a single
gene for resistance to IPO323 in
Flame. If this prediction is correct,
F 3 families from resistant or
susceptible F 2 individuals are
expected to be uniformly resistant
or susceptible, whereas
intermediate F 2 individuals should
produce F 3 families segregating 1:3
for IPO 323
resistance:susceptibility.
To investigate whether
Hereward carries the same IPO323
resistance gene as Flame, F 2
progeny of crosses between
Hereward and Longbow and
between Hereward and Flame will
be tested as detached leaves. The
Hereward x Longbow cross will
determine whether Hereward’s
resistance is controlled by a single
gene. The Hereward x Flame cross
will test for allelism. The results
from both tests will be presented.
As IPO323 avirulence is
controlled at a single locus (Kema
et al., 1999) and Flame’s resistance
to this isolate may be due to a
single gene, we hypothesize that a
gene-for-gene relationship exists
between Flame and IPO323. To
confirm this hypothesis, we are
testing 61 progeny isolates from the
IPO323 x IPO94269 cross on Flame
and Longbow as detached leaves.