Abstract
Cultivated six-rowed naked barley (Hordeum vulgare ssp. hexastichon var. nudum Hsü) is the oldest cultivated barley in China. We used 35 simple sequence repeat (SSR) markers selected from seven barley linkage groups to study the genetic diversity, geographical differentiation and evolutionary relationships among 65 H. vulgare ssp. hexastichon landrace accessions collected from the Qinghai-Tibet plateau of China, 25 accessions from Tibet (TB), 20 from Qinghai (QH) and 20 from Ganzi (GZ) prefecture in Sichuan province. At the 35 SSR loci we identified 248 alleles among the 65 accessions, 119 (47.98%) of the alleles being common alleles. We also found that the TB accessions possessed 47 private alleles, about 1.5 times more than the 31 private alleles found in the QH accessions and about 5 times more than 9 private alleles found in the GZ accessions. Generally, the TB accessions showed significantly higher genetic diversity than either the QH or GZ accessions whereas no significant difference in genetic diversity was found between the QH and GZ accessions. Partitioning analysis of genetic diversity showed that about 81% of the total variation was due to within-subgroup diversity and about 19% was clearly accounted for by geographical differentiation among the three subgroups. The distributions of alleles for most loci (71.4%) were significantly different among the three subgroups and geographical differentiation could be found according to the distribution of SSR alleles. Cluster analysis indicated that most of the accessions could be clustered into groups which basically coincided with their geographical distribution. These results suggest that Tibet might be a center of genetic diversity for cultivated barley, the cultivated six-rowed naked barley on the Qinghai-Tibet plateau of China may have evolved in Tibet and spread to Qinghai and then to Ganzi prefecture of Sichuan province.
Highlights
Barley (Hordeum vulgare L.) is one of the oldest cultivated crops in the world and studying genetic diversity and evolutionary relationships in barley is important for the effective conservation and utilization of barley genetic resources
No allele was detected at the HVM44 locus in the QH accessions and HVM14 locus in the GZ accessions and only one allele each was detected for the HVM34, HVM49 and HVM60 loci in the TB accessions, the HVM64 locus in the QH accessions and the HVM23, HVM49 and HVM64 loci in the GZ accessions
In group D the QH and GZ accessions were clustered into their own separate groups at a genetic similarity level of 0.8 (Figure 1). These results clearly reveal the geographical differentiation of nudum barley landraces in the Qinghai-Tibet plateau and their genetic relationship
Summary
Barley (Hordeum vulgare L.) is one of the oldest cultivated crops in the world and studying genetic diversity and evolutionary relationships in barley is important for the effective conservation and utilization of barley genetic resources. Many studies have demonstrated that Tibetan wild barley populations were clearly different from the Fertile Crescent wild barley in respect to their distribution, ecology, morphology, archaeology, cytogenetics and isozyme complement (Xu, 1975, 1982; Zhou, 1981; Shao, 1982; Yao, 1982) This supports the hypothesis of separate evolutionary systems leading to Tibetan two-rowed wild barley becoming the ultimate progenitor of Chinese cultivated barley, Tibetan six-rowed wild barley being an intermediate form in the processes of transforming two-rowed wild barley to six-rowed cultivated barley (Xu, 1982). Study on genetic diversity and geographical differentiation of cultivated six-rowed naked barley landraces from the Qinghai-Tibet plateau will be useful in understanding the evolutionary relationship of barley
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