A century of breeding - is genetic erosion a reality?

Barley (Hordeum vulgare L. ssp. vulgare) is an important crop in the Nordic and Baltic countries, where it is mainly used for feed and malt. Commercial breeding of barley has been carried out in this region for more than a century, and landraces have been completely replaced by pure line cultivars. There is a concern that plant breeding might lead to a severe reduction of genetic diversity, so-called genetic erosion, since commercial breeding was initially based only on a few successful selections from landraces. The consequences of such erosion would affect plasticity of the crop, which might reduce its ability to adapt to future agriculture and consumption demands and increase the vulnerability to epidemics. The aim of this study was to evaluate the degree of putative genetic erosion and relationships in Nordic and Baltic barley material. A large collection representing landraces and cultivars from the end of the 19th century up to modern material were analysed by isozymes and DNA markers. In addition, field trials were performed in order to observe changes in the diversity of agronomic traits. General indications of a decrease in diversity were observed. A loss of less common alleles was found in molecular markers and a significant decrease of variability was detected for most agronomic traits. However, the molecular markers failed to prove significant diversity changes in the material as a whole. New alleles, not present in Nordic and Baltic landraces and old cultivars, were found in modern material. Differences in the magnitude of diversity varied depending of country and region (North vs South) of origin and row type of the crop. Some of these diversity changes were also significant in the molecular makers, for example a significant decrease in material from the southern part of the region was observed. The two-rowed and six-rowed cultivars of this region were well differentiated not only by agronomic data, but also by DNA markers. They demonstrated differences at chromosome regions distant from the inflorescence determinating genes. While agronomical data separate modern material from landraces and old cultivars fairly well, DNA markers achieved this for most of the countries only when the material was analysed separately by country. The main conclusion of this study is that breeding in Nordic and Baltic countries has decreased diversity at some traits, but overall diversity of the crop has not changed significantly. However, the landraces and old cultivars of the region should still be considered as valuable diversity sources since some of the loci found there are not present in modern materials.