The population structure of accessions of barley landraces (BLR) (Hordeum vulgare L ssp. vulgare) from Syria was investigated using genetic markers. Barley landraces are old, diverse cultivars of barley which have evolved under cultivation without much directed selection. BLRs have been shown to outperform modern cultivars under low input conditions in Syria due to the level of local adaptation and population buffering (i.e. the ability to compensate the failure of a component by a genetically different component of the same population) based on a high level of diversity within landraces.
The purpose of the present study was to identify suitable genetic markers, to use these to characterise the population structure and diversity of barley landraces, and to investigate how population structure is influenced by environmental conditions. Results were compared with those achieved for accessions of wild barley (Hordeumvulgare ssp. spontaneum C. Koch) and modern cultivars in order to investigate the influence of domestication and cultivation on mating system and population structure. Implications of the results for breeding strategies in low input agriculture and for conservation strategies were investigated.
wo recent accessions of wild barley and 15 recent accessions of BLRs were available from Syria, where landraces are still under cultivation. Seven earlier accessions of the same landraces from Syria were available from gene banks. Modern cultivars and progeny of known pedigree were available from barley breeders. Genetic indices of accessions were analysed using three contrasting types of genetic markers, morphological, isoenzyme and molecular markers, respectively. Standard methods of population genetics were used to analyse the population structure of accessions. Environmental conditions of the sampling sites were analysed using the geographical information system ArcView.
Results showed that BLRs are predominantly inbreeding populations with a low outcrossing rate of 1.7%. The same outcrossing rate has been reported for wild barley, so that it can be assumed that domestication has not influenced the outcrossing rate. Recently collected BLRs showed a high level of diversity and a regionally localised and geographically variable population structure. Harsh environmental conditions seem to increase diversity of BLRs. Genetic diversity may have been lost through the process of domestication. More diversity was found within populations of wild barley, while BLRs showed a higher proportion of diversity between accessions, for two of the three molecular markers used. Little diversity was found between modern cultivars, and no diversity within them. This may imply that modern breeding methods have led to a loss of diversity in the current gene pool. Gene flow between accessions within regions was high, but low between more distant regions, implying little seed exchange between farmers in different regions. However, it seemed that intensive extension work may lead to increased seed exchange over long distances and thus may decrease the level of local adaptations. Finally, a dramatic loss of genetic diversity of BLR accessions was found with increasing storage time in ex situ gene banks, suggesting the presence of genetic bottlenecks associated with the rejuvenation of ageing seeds accessions. Genetic diversity levels of recently collected BLRs support the implementation of in situ conservation strategies.