Strategies for the Development of Fusarium-resistant Wheat in Canadian Breeding Programs

摘要

Fusarium head blight (FHB), caused principally by Fusarium graminearum Schwabe remains one of the most serious fungal diseases affecting cereals in Canada. Diverse strategies have been employed in Canadian breeding using conventional, molecular, and alternative methods. Lines with good FHB resistance have been developed using conventional techniques in the main class of Canadian wheat. The difficulty has been to combine resistance with the stringent quality requirements of the Canadian marketing system. In 2003, one third of the entries in the CWRS cooperative trials rated resistant or moderately resistant to FHB and some were also leaf and stem rust resistant. To date, most spring wheat breeding programs have relied heavily on the Chinese resistance source, Sumai 3 and its Ning derivatives, while the winter wheat program in eastern Canada has used the Brazilian cultivar Frontana. Other sources of resistance have been identified including several Triticum spp. such as T. monococcum, T. miguschovae, and T. timopheevi in addition to Aegilops speltoides, Ae. squarrosa, Thinopyrum intermedium and a tritordeum cross between Triticum durum and Hordeum chilense. The objectives of the durum wheat breeding program are to 1) exploit the available resistance within durum wheat and 2) to move FHB resistance from other wheat relatives into durum wheat. A few lines have been identified, all with the breeding line DT 696 in their pedigree, which are less severely affected by FHB. Other sources of improved resistance include the tetraploid wheats T. dicoccoides and T. carthlicum, as well as hexaploid common wheat, Sumai 3 and Maringa. The principal molecular breeding study is working to pyramid QTL for FHB resistance on 2DL, 3BS, 4B, 5AS, 6B with Lr21 and resistance to wheat midge. There are 49 BC2F2 plants homozygous for several FHB resistance genes, midge resistance and Lr21, which will be field- evaluated in the 2004 season for the first time. Recently, microarray-based genome profiling has been used to uncover novel genes which are up- or down-regulated during the course of pathogen attack. To date, specific subsets of responsive genes were detected for glume and lemma tissue. Using microgenomics, a gene expression signature may possibly be used as a diagnostic tool to identify plant resistance genes. Some alternative strategies have revealed unexpected variation induced in plants subjected to stresses from repeated cycles of WSM or Barley Yellow Dwarf (BYD)-plus-WSM disease pressure. This protocol of subjecting plants to repeated cycles of systemic disease pressure has been named Stress-Directed Selection (SDS).