Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

148
Field Resistance of Wheat to Septoria Tritici Leaf Blotch,
and Interactions with Mycosphaerella graminicola
Isolates
J.K.M. Brown, 1 G.H.J. Kema, 2 H.-R. Forrer, 3 E.C.P. Verstappen, 2 L.S. Arraiano, 1 P.A. Brading, 1 E.M. Foster, 1 A.
Hecker, 3 and E. Jenny3 1 John Innes Centre, Norwich, UK
2 DLO-Research Institute for Plant Protection, Wageningen, The Netherlands
3 Swiss Federal Research Station for Agroecology and Agriculture, Zürich, Switzerland
Abstract
The resistance of 71 varieties of bread wheat to six isolates of Mycosphaerella graminicola was studied in field trials in
the Netherlands, Switzerland, and the UK, carried out over three years. There was a wide range of Septoria tritici infection.
Some varieties had especially good resistance, including lines from Europe (especially Switzerland) and Latin America. Many
interactions between varieties and isolates were detected. In particular, 27 varieties of diverse origins were specifically
resistant to the isolate IPO323. Variety-by-isolate interactions were stable over years and locations. The existence of these
interactions and the fact that they are stable over environments implies that certain widely used resistances to Septoria tritici
might break down through the evolution of specific virulence in the fungus. Breeders should take these interactions into
account in their efforts to develop varieties with durable resistance.
Septoria tritici leaf blotch is
now the most economically
important foliar disease of wheat in
Europe, and controlling it with
fungicides costs several hundred
million dollars a year. Resistance to
septoria tritici leaf blotch is
therefore a major target for most
European wheat breeders.
However, if resistant varieties are
to be economically worthwhile,
resistance must be both effective
and durable.
Strong, specific interactions
between wheat varieties and
isolates of the pathogen,
Mycosphaerella graminicola, have
been found in both seedlings and
adult plants (Kema and van
Silfhout, 1997), while the resistance
of at least one variety, Gene, has
“broken down” through the
evolution of a virulent pathogen
population (Mundt et al., 1999).
This means that breeders need to
know not only which varieties may
be good sources of resistance in
breeding programs, but also
whether or not resistance genes in
these varieties are at risk from
virulent isolates of M. graminicola.
This paper reports a series of
field trials carried out in England,
The Netherlands, and Switzerland
between 1994 and 1997. The aims
were to investigate resistance to
septoria tritici leaf blotch in a
representative set of European
varieties, to evaluate potential new
sources of resistance, to study the
responses of varieties to different
isolates of M. graminicola and to test
the stability of variety-by-isolate
interactions over a range of
environments.
Materials and Methods
A total of 71 wheat varieties of
diverse origins were included in
the field trials. The majority were
cultivars or breeding lines
developed by European breeders.
Most of these were winter wheats.
Several varieties that are potential
sources of septoria tritici leaf blotch
resistance were also included, as
were a number of varieties that are
parents of precise genetic stocks
held by the John Innes Centre.
Trials were inoculated with six
monospore isolates of M.
graminicola from the IPO-DLO
collection. Six trials were
conducted, three in the
Netherlands, one in Switzerland,
and two in England. Each trial was
sown in a split-plot design with
two replicate blocks. Within each
block, there were five or six main