The effect on gliadin allele composition of environmental selection and selection for seed size in a population formed from a multi-line cross of bread wheat varieties

E.V. METAKOVSKY and S.F. KOVAL

Institute of General Genetics, Moscow. and Institute of Cytology and Genetics, Novosibirsk, USSR.

Introduction

There are several methods of selection of the best genotypes available for the cereal breeding programmes. One of them involves growing a hybrid population for several generations in the field. Natural selection favours those genotypes which are most adapted to the particular field conditions and decreases or eleminates the less adaptive ones¹⁾. Therefore the selective value of a character can be measured by determining the change in its frequency in the population before and after selection. This approach was successfully used in studies of hybrid populations in barley (2) and maize (3), where the polymorphism of sertain enzymes was strongly affected by natural selection. We used the same approach and found differencies in adaptive value of several alleles of Gld IB and Gld ID, two main complex loci of wheat controlling the synthesis of gliadin, the storage protein of the seed.

Methods

The initial population was created by a three-step hybridization of 8 varieties of spring wheat T. aestivum : Saratovskaya 210, Dalnevostochnaya, Kzyl Bas, Zarnitsa, Kirgizskaya Yubileinaya (all from USSR), Solo (FRG), Norrona (Norway), Siete Cerros 66 (Mexico). In step one, 4 pairs of parents were crossed and the resulting F₁ progeny were crossed with each other in step two. In the third step, the secondary hybrids were crossed, giving progeny which contained genes from all eight parents. At each step at least 30-40 maternal spikes and 50-80 paternal plants were used for each cross. The final hybrid material was propagated in a glasshouse (2 first generations of self-pollination) to obtain seeds of the initial population (IP). These seeds were sown in the field at the rate of 20 cm² for one plant, in the north forest-steppe of Novosibirsk, USSR. All plants of a harvest without any exception were thrashed together. 500-1,000 seeds (in different years) were randomly selected from the harvested grain and used for sowing.

There are two variant types of population originated from IP, the first having arisen only by environmental selection during 4 years (NS). The second is natural plus artificial selection for grain size and marketability being about 33% of all seeds (NAS). In the NAS variant the random sample for sowing was taken from the mass of seeds after artificial selection.

The extraction of gliadin with 70% ethanol and single-seed electrophoresis was performed as described earlier⁴⁾. Alleles in parental varieties were identified by analysis of F₂ seeds of the primary crosses (self-pollination of some F₁ plants). Gld 1B and Gld 1D are the main gliadin-coding loci localized on chromosomes 1B and 1D, respectively. This nomenclature and numeration of alleles are in accordance with the catalogue of blocks of gliadin components⁴⁾.

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