[Genealogic analysis of the resistance of winter wheat to common bunt]

Comparative genealogical analysis of North American (the United States and Canada) and Eastern European (Russia and Ukraine) winter wheat cultivars resistant and susceptible to common bunt has been performed. Analysis of variance applied to North American wheats has demonstrated that resistant and susceptible cultivars significantly differ from each other with respect to the contributions of common ancestors. The contributions of Oro (Bt4 and Bt7), Rio (Bt6), White Odessa (Bt1), and Florence (Bt3) to the resistant cultivars are significantly higher than their contributions to the susceptible ones. This demonstrates that the use of these resistance donors in wheat breeding for several decades has been effective. The contribution of PI-178383 (Bt8, Bt9, and Bt10) is considerably higher in the group of resistant cultivars bred after 1965. The mean contributions of Federation (Bt7) and Nebred (Bt4) are significantly higher in the group of resistant cultivars obtained before 1965; however, the differences in the contributions of these donors between new resistant and susceptible cultivars became nonsignificant. Among the Russian and Ukrainian cultivars, there are differences between groups of resistant and susceptible cultivars from different regions determined by the differences between the regional populations of the pathogen in racial composition. In the northern region, the contributions of the wheat grass (Agropyron glaucum) and the rye cultivar Eliseevskaya are significantly higher in the resistant cultivars; in the southern region, a local cultivar of the Odessa oblast is the prevalent resistant cultivar. In addition, cultivar Yaroslav Emmer is likely to be effective in the northern region; and foreign sources (Oro, Florence, Federation, and Triticum timopheevii), in the southern region. Very few sources of vertical resistance to common bunt are used for winter wheat breeding in Russia and Ukraine. The decrease in genetic diversity in favor of a few identical genes may cause adequate changes in the pathogen population and subsequent proliferation of the pathogen on the genetically identical substrate. A new interpretation of the resistance of line Lutescens 6028 as a source of new genes, Bt12 and Bt13, is suggested. Both genealogical and segregation analyses have shown that the genes determining the resistance of this line may be identical to those described earlier (Bt1, Bt3, Bt4, Bt6, and Bt7); and the high resistance of this line is determined by a combination of these genes.