RESUMEN
Powdery mildew, caused by Blumeria graminis (syn. Erysiphe graminis) f. sp. tritici, is an important disease of bread wheat (Triticum aestivum) in many countries. The CIMMYT bread wheat line Saar has exhibited a high level of partial resistance to powdery mildew in field trials conducted in Europe, Asia, and South America, and represents a valuable source of resistance in wheat breeding. A set of 114 random F5 inbred lines from the cross Saar × Avocet-YrA (susceptible) were evaluated in replicated field trials at two locations in southeastern Norway to determine the number of genes involved in partial resistance to powdery mildew. Narrow-sense heritability estimates were high (0.83 to 0.92). Based on both quantitative and qualitative genetic analyses, the minimum number of genes with additive effects segregating for powdery mildew resistance in the population was four. Transgressive segregation indicated that Avocet-YrA might have contributed one minor gene for resistance. It is concluded that partial resistance to powdery mildew in Saar is controlled by at least three genes. Such resistance conferred by multiple genes having additive effects is expected to be durable.
RESUMEN
ABSTRACT Near-isogenic lines (NILs) with resistance for scald in seventh generation backcross with 'Ingrid' as recurrent parent (RP) were tested with seven differential isolates of Rhynchosporium secalis in Norway and Canada. NILs of 'Turk', 'Brier', 'CI 8162', 'La Mesita', 'Hispont', 'Atlas 46', 'Modoc', 'Hudson', 'Abyssinian', 'Steudelli', and 'CI 2222' also were evaluated for field reactions. The genetic characterization of the NILs (degree of isogeneity with Ingrid) and with each other was carried out. The molecular marker pattern shows that the backcrossing program has resulted in from 86.3 to 100% RP genome in the NILs, depending on the marker system. On an average, 96% RP genome was found in the NILs. There were certain consistent (pairwise) differences between the NILs and RP on chromosomes 3H and 7H. Both chromosomes are known to contain loci conferring resistance to R. secalis, indicating successful introgression from the donors into the NILs. Approximately two-thirds of the observed RP-NIL polymorphisms were linked to the assumed resistance in the NIL. Based on the marker and phenotypic analyses of the NILs, suggestions for a more appropriate and updated terminology of genes for resistance to R. secalis in barley are made. The proposed changes in nomenclature also indicate the differentials that are available as NILs and those lacking.