Homozygous genotypes for apple breeding: a feasible approach?

摘要

Malus x domestica (apple) is a temperate fruit species with several breeding disadvantages such as heterozygosity, self-incompatibility and long-lasting juvenility. In theory, homozygous apple genotypes could improve apple breeding efficiency, especially by facilitating parent selection. They would also be valuable for genetic studies, mapping and test crosses. However, the development and application of these genotypes for breeding is not so obvious in practice. In 'Braeburn', pollen-derived genotypes were obtained after in vitro anther culture. However, efficiency was generally low. Homozygosity and origin of the genotypes were determined by SSR-markers: all genotypes were homozygous derivatives of 'Braeburn'. In the field these homozygous genotypes showed an aberrant growth and fertility, preventing their use in breeding programmes. The ploidy of the genotypes was determined by flow cytometry; diploids, triploids as well as tetraploids were present. This study has shown that although homozygous genotypes can be obtained in 'Braeburn', their value for breeding is severely reduced by their inferior fertility and vigor.