In Ethiopia, barley is generally grown in two different planting seasons per year: during the long rainy season (Meher) and the short rainy season (Belg). The aim of the present study was to assess for the first time the role of this 'two-season system' on the structure of the genetic diversity of the Ethiopian barley landraces. We characterised 3,170 individual genotypes from 106 landrace populations using eight morphological spike traits. The diversity within population was higher in the season where barley is more important (Belg), and in general, where its cultivation is in larger plots because of weaker 'competition' with others crops. This indicates that barley diversity has a complex relationship with variations in the surrounding agro-ecosystem. Overall, the divergence between the two seasons was quite small (3.4%), suggesting that seed flow does not occur independently across the years within the two seasons. This would affect the amount of mutations and historic recombination that have accumulated within these populations.

BackgroundAmong the cereal crops, barley is the species with the greatest adaptability to a wide range of environments. To determine the level and structure of genetic diversity in barley (Hordeum vulgare L.) landraces from the central highlands of Ethiopia, we have examined the molecular variation at seven nuclear microsatellite loci.ResultsA total of 106 landrace populations were sampled in the two growing seasons (Meher and Belg; the long and short rainy seasons, respectively), across three districts (Ankober, Mojanawadera and Tarmaber), and within each district along an altitudinal gradient (from 1,798 to 3,324 m a.s.l). Overall, although significant, the divergence (e.g. FST) is very low between seasons and geographical districts, while it is high between different classes of altitude. Selection for adaptation to different altitudes appears to be the main factor that has determined the observed clinal variation, along with population-size effects.ConclusionsOur data show that barley landraces from Ethiopia are constituted by highly variable local populations (farmer's fields) that have large within-population diversity. These landraces are also shown to be locally adapted, with the major driving force that has shaped their population structure being consistent with selection for adaptation along an altitudinal gradient. Overall, our study highlights the potential of such landraces as a source of useful alleles. Furthermore, these landraces also represent an ideal system to study the processes of adaptation and for the identification of genes and genomic regions that have adaptive roles in crop species.

Barley (Hordeum vulgare L.) has great adaptability to a wide range of environments. To determine genetic diversity in barley landraces, a total of 43 landrace populations were randomly sampled from the farmers' field on plant basis and characterized for eight qualitative traits; namely, kernel row number, spike density, lemma awn barb, glume color, lemma type, length of rachila hair, kernel covering and lemma/kernel color. Morphological diversity was determined by the Shannon-Weaver index (H'). Overall barley landrace populations showed an average diversity index of 0.59, implying large diversity for the populations. Selection for adaptation to different altitude classes appears to be the main factor that has determined the observed variation, along with population-size effects. The result showed that barley landraces from Gamo highlands, Ethiopia are constituted by highly variable landraces that have large within-population diversity. These landraces are also shown to be locally adapted, with the major driving force that has shaped their population structure being consistent with selection for adaptation along an altitudinal gradient. Overall, this study highlights the potential of such landraces as a source of useful genes that can be exploited in crop improvement programmes.