Gliadin genotypes worldwide for spring wheats (Triticum aestivum L.) 1. Genetic diversity and grain-quality gliadin alleles during the 20th century

High genetic diversity (H = 0.85 ± 0.03) of spring common wheats (290 cultivars from nine countries, four continents) was discovered through the identification of alleles at the gliadin-encoding (Gli) loci. There were no indications of the existence of genetic erosion (narrowing of polymorphism with time) either for wheat germplasm studied throughout the 20th century, or in the group of cultivars bred in any country. At the same time, there was a significant change of the frequency of occurrence, in wheat germplasm of Australia, Canada, Mexico, Nordic countries, Spain, and the former USSR, of certain gliadin alleles related (as shown earlier) to end-use wheat quality, mainly to dough strength. The increase in frequency, in genotypes of groups of more recent cultivars, of gliadin alleles positively influencing dough strength (Gli-B1b, Gli-B1d, and Gli-B2c) caused a loss of genetic diversity at the corresponding Gli loci. It is suggested that these alleles may serve as an indirect targets of breeders' selection for dough quality. Mechanisms of the involvement of some allelic variants of the Gli loci in the manipulation of dough quality are discussed.