Ribosomal DNA spacer-length polymorphisms in three samples of wild and cultivated barleys and their relevance to the origin of cultivated barley
X. Li, C. Xu and Q. Zhang
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Volume 123 Issue 1 Page 30 - February 2004
This study was conducted to provide additional data for evaluating two important issues surrounding the origin of cultivated barley: (i) the level of genetic diversity of the two-rowed wild barley from Tibet, and (ii) the distribution of rDNA allele 104 in wild and cultivated barleys in the Occidental region. A total of 198 accessions consisting of three distinct samples were used: 82 entries of two-rowed wild barley from Tibet, 57 accessions of two-rowed wild barley from 8 countries with a broad range of representation of two-rowed wild barley in the world, and 59 landrace accessions from four countries representing a part of the barley-growing areas in the Middle East. These were assayed for rDNA spacer-length variants (slvs). In all, 27 rDNA space length phenotypes were detected, from which 10 slvs were identified as alleles at the two rDNA loci. The two-rowed wild barley samples from Tibet had the lowest level of genetic variation as evaluated by rDNA polymorphism. Together with results of previous studies, the two wild forms (two-rowed and six-rowed) from Tibet could not account for the large genetic diversity observed in the cultivated barley of this region, suggesting that Tibet is unlikely a centre of origin for cultivated barley. In samples from the Occidental region, allele 104 of Rrn2 was very rare in wild barley, but occurred at the highest frequency in cultivated barley, while the reverse is the case for allele 107, which is consistent with previous results. The implications of such a contrasting distribution of these rDNA alleles between wild and cultivated barleys in the origin and evolution of cultivated barley were discussed.