A catalog of gliadin alleles: Polymorphism of 20th-century common wheat germplasm

Abstract

A new, improved version of the catalog of 182 alleles at the six Gli loci of common wheat (T. aestivum L.) shown in electrophoregrams of 128 standard genotypes was used for analysis of 1060 cultivars and lines bred in the 20th century. The most frequent alleles in the studied germplasm occurred with frequencies of 18%–40%, with 30 unique alleles, one in each cultivar. Extremely high genetic diversity was found (average H for the six main Gli loci was 0.870±0.046), nearly identical in winter (H=0.831) and spring (H=0.856) wheats but differing among 28 groups of cultivars released in 22 countries. Each country or region was characterized by its own specific set of the most frequent Gli alleles, and the 28 cultivar groups formed five main relationship clusters if polymorphism at the six Gli loci was considered. However, different levels of similarity between groups of cultivars were found if polymorphism of the A, B, or D genomes of common wheat was tested separately. In general, the 20th century germplasm of common wheat was differentiated and structured by country or region and cultivar type (spring or winter). Each elemental genome (in particular, A and D) contributed to the structure of the polymorphism studied. We propose that the structure of the wheat germplasm was a result of natural selection under the eco-climatic conditions of cultivation specific to each country or region. As many as 27.4% of cultivars studied violated the requirement of the DUS rules for uniformity, being represented by mixtures of two or more closely related genotypes. However, the composition of a cultivar as a set of related but different genotypes may contribute to its adaptivity, and thereby to the known high plasticity of common wheat.