Investigations related to resistance to take-all and Stagonospora nodorum leaf blotch in wheat

Because of the absence of any effective varietal resistance to take-all (Gaeumannomyces graminis var. tritici) in cultivated wheat (Triticum aestivum), relatives of wheat could be an importance source of resistance for wheat breeding programs. A greenhouse bioassay to screen for resistance was developed and four small grains were examined for relative susceptibility. The order of susceptibility was wheat > barley > rye ≥ oats. The bioassay was used to screen wheat—alien chromosome addition and substitution lines of Hordeum vulgare, Hordeum chilense, and Haynaldia villosa for useful levels of resistance. Any improved levels of take-all resistance were not detected in any addition and substitution lines. However, the addition line sets for H. vulgare and H. chilense were incomplete. Therefore, take-all resistance in the alien species may be on a chromosome that was not tested, polygenic with genes on different chromosomes, or masked by the wheat genome. Stagonospora nodorum blotch (SNB) can cause serious yield and quality losses of wheat in many countries worldwide. Although there are other control methods, host resistance is the most desirable. To determine inheritance of resistance and allelism, three winter wheat cultivars Betty, Heyne, and 2163 with moderate levels of resistance to the leaf phase of SNB were crossed with one of three susceptible lines Larned, KS96WGRC39, or Newton and intercrossed in all possible combinations, including reciprocals. The parents, F₁, F₂, and F₃ generations were screened in the greenhouse as 4-wk-old seedlings. Cytoplasmic effects were not detected in any cross. The F₁s of Betty × Larned and Heyne × KS96WGRC39 showed dominance for resistance. A single dominant resistance gene was identified in the cultivar Betty, and probably in Heyne. The allelism test for Betty and Heyne indicated that they have different resistance genes. No estimation for the number of genes in the cultivar 2163 was possible. To determine the effect of temperature on resistance to SNB, seedlings of the winter wheat cultivars Newton, AGSECO 7853, and Heyne were tested in three temperature regimes. The reaction of AGSECO 7853 was intermediate between Heyne and Newton at high temperature, as susceptible as Newton at medium temperature, but more susceptible than Newton at low temperature. Therefore, the reaction of AGSECO 7853 relative to Newton was temperature-sensitive.