DISEASES AND INSECTS

In western Canada, there are a large number of diseases and insects that have the potential to cause economic losses in winter wheat ( Table 2 ). Plant resistance is the most environmentally safe, reliable, and cost effective means available for controlling these diseases and insects. However, existing winter wheat cultivars have poor resistance to most of the diseases and insects prevalent in this region ( Table 2 ). The poor resistance of western Canadian winter wheat cultivars has not been due to the absence of satisfactory sources of genetic resistance. Rather, the problem has been the lack of resources to mount sustained breeding programs that give the production of disease and insect resistant cultivars a high priority.

The high level of cultivar disease and insect resistance that is an accepted part of spring wheat production in western Canada was achieved only after many years of intensive, coordinated efforts among wheat breeders and pathologists. Similar levels of resistance could be incorporated into winter wheat. However, as was the case with spring wheat, the development of cultivars with a broad spectrum of disease and insect resistance can be expected to proceed slowly and often in small increments. The efforts to develop rust resistant winter wheat cultivars provides an example of the difficulties winter wheat breeders have encountered in living up to the high standards of insect and disease resistance maintained by spring wheat breeders.

The expansion of winter wheat out of its traditional production area in Alberta has focused considerable attention on the need for rust resistant cultivars. Rust does not overwinter on the Canadian prairies and each year must be reintroduced from the southern USA. For most of western Canada, winter wheat reaches maturity before the rust inoculum has a chance to build up to significant levels. Since rust usually enters the southeast corner of the Canadian prairies first, the highest risk of damage exists in southern Manitoba and southeastern Saskatchewan.

In the northern part of the USA Great Plains region, all the major winter wheat cultivars are susceptible to leaf rust and most have poor levels of stem rust resistance. Consequently, rust resistant cultivars adapted to this region are not available for use as parents in Canadian breeding programs. So far efforts to transfer rust resistance from Canadian spring wheat cultivars to winter wheat have not been successful. In western Canada, Norwin and CDC Kestrel winter wheat cultivars have a slow rusting characteristic that delays the development of stem rust epidemics by a week to ten days. CDC Kestrel and breeding lines with this slow rusting reaction have had an average 40 percent yield advantage over Norstar in trials grown under favorable moisture and heavy, late rust epidemics in Saskatchewan and Manitoba. However, even with a yield advantage of this magnitude in the presence of a rust epidemic, the requirement for a resistant rust rating has prevented the disease evaluation team of the Prairie Registration Recommending Committee for Grain ( Figure 3 ) from "supporting" slow rusting winter wheat lines for registration as cultivars for production in western Canada.

GRAIN YIELD

A farmers' income per acre (hectare) is determined by grain yield and price per bushel (tonne). The price that the farmer has received for No. 1 and 2 Canada Western Red Winter wheat has been similar to that of No. 3 Canada Western Red Spring wheat. Therefore, the top two premium wheat grades have been conceded to the Canada Western Red Spring wheat class and the price premium paid for these grades must be compensated for by higher yields if the Canada Western Red Winter wheat class is to be an economic option for the farmer (see Chapter 25 ).

The price of Canada Western Red Winter wheat has been closer to that of the high yielding Canada Prairie Spring than the Canada Western Red Spring wheat class. Therefore, unless there is new evidence that price per bushel (tonne) can be increased to reflect superior quality, winter wheat breeders must comply with long term breeding objectives that will allow Canada Western Red Winter wheat to remain competitive in markets that are priced similarly to that of Canada Prairie Spring wheat. This can only be interpreted to mean that winter wheat breeding objectives must reflect the lower protein and higher yield targets of the Canada Prairie Spring class.

As a class, Canada Prairie Spring wheat cultivars have a protein concentration that is two percent lower and a grain yield that is 20 percent higher than Canada Western Red Spring wheat cultivars. This reflects a trade off of 10 percent gain in grain yield for each percentage point sacrificed in grain protein concentration of spring wheat.

Norstar winter wheat has had a 25 to 36 percent yield advantage over cultivars from the Canada Western Red Spring wheat class. Release of the winter wheat cultivar CDC Kestrel in 1991 established that the high yield potential of semi-dwarf wheat can be combined with good winter hardiness to further raise the yield advantage held by winter wheat in western Canada. CDC Kestrel has maintained a yield similar to Norstar under high drought stress conditions. Under more favorable moisture conditions, CDC Kestrel has yielded 22 percent higher than Norstar. Given the realities of the marketplace, winter wheat breeders must place continued emphasis on consolidating and improving this yield advantage while maintaining their efforts to improve other important agronomic and quality traits.