INTRODUCTION

    World plant breeders, producers and the public are increasingly concerned that modern plant breeding is increasing the risk to sustainable crop production because of a narrowing of the gene pool used to produce new cultivars (Tripp, 1996).  Such reduction influences both the vulnerability of crops to biotic stresses such as pests and diseases, and abiotic stresses such as the crop’s ability to respond to climate or agricultural practice (FAO, 1998).  Several types of data are required to document the changes that may have occurred in the genetic diversity of the major Canadian agricultural crop species.  It is well documented that significant advances in agronomic improvements of Canadian crops have occurred, for example, soybean (Morrison et al., 2000). Recent advances in molecular techniques have facilitated studies in crop genetic diversity (Karp et al., 1997).  Many studies suggested the reduction in the genetic diversity accompanying plant improvement has been negligible (Donini et al., 2000, Christiansen et al., 2002, Fu et al., 2003, Fu et al., 2003).  For example, Donini et al. (2000) showed that plant breeding resulted in a qualitative rather than quantitative change in genetic diversity of 55 dominant UK winter wheat varieties released from 1934 to 1994.  These examples appear to refute the concern that by reducing diversity modern plant breeding is increasing the risk to sustainable crop production.  Very few studies combine genotypic and phenotypic evaluations of genetic diversity for many cultivars over a period of time. This study addresses this deficit for Canadian wheat (Triticum aestivum L.)

    Canadian wheat production became important about 1605 with the spread of new settlements across Canada.  Early production problems were numerous and generally associated with major epidemics of plant diseases, insects or lack of adaptation.  One of the first major varieties successfully grown was Red Fife.  Dominant in the 1840's, it was grown in many regions because it had good milling and bread-making quality.  Over the next 160 years, Canadian wheat breeders focused on improved yield and early maturity in such cultivars as Marquis, Rescue, Columbus and AC Barrie.  Advances also occurred in resistance to many plant diseases, insects, better adaptation to more regions across Canada, and improved quality.  To date, breeding programs have developed over 100 wheat cultivars, most of which have had a significant impact on the economy of the Canadian prairies (DePauw et al., 1995).

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