Wheat midge resistance: breeding and genetics

Orange wheat blossom midge (OWBM, Sitodiplosis mosellana Géhin) is a damaging insect pest of wheat.
Tools for integrated OWBM management include midge resistant varieties, early seeding of spring wheat,
foliar insecticide application, and the parasitic wasp Macroglenes penetrans (Kirby). OWBM resistant
varieties have been registered in Canadian spring and durum wheat classes. The genetic basis of this
resistance is the gene Sm1, which is the only described OWBM resistance gene. Sm1 is easily selected
based on phenotype with trained personnel but DNA markers are desirable for breeding. A saturated
genetic map of the Sm1 region of chromosome arm 2BS has been developed. Progress on map-based
cloning of Sm1 will be reported. Oviposition deterrence is another mechanism of managing OWBM
damage with host genetics. OWBM oviposit fewer eggs on spikes of deterrent wheat lines relative to nondeterrent
wheats. Research to date indicates that deterrence is the result of a volatile compound(s).
Reduced midge damaged kernels can also arise from aberrant egg laying behavior where eggs are
oviposited on the rachis rather than the florets. Oviposition deterrence has been identified in Canadian and American spring wheat varieties, a few American winter wheat varieties, and a few durum wheat lines. Present and future research in this area will be discussed. Testing of wheat accessions is also underway to search for additional resistance genes. The genetic research underway will assist in the development of varieties with improved OWBM resistance coupled with oviposition deterrence.