A comparative analysis of genetic polymorphism in wild and cultivated barley from Tibet using isozyme and ribosomal DNA markers

Abstract

This study was conducted to address some of the issues concerning the possible significance of Tibet in the origin and evolution of cultivated barley. A total of 1757 barley accessions from Tibet, including 1496 entries of Hordeum vulgare ssp. vulgare (HV), 229 entries of the six-rowed wild barley H. vulgare ssp. agriocrithon (HA), and 32 entries of the two-rowed wild barley H. vulgare ssp. spontaneum (HS), were assayed for allozymes at four esterase loci. A subsample of 491 accessions was surveyed for spacer-length polymorphism at two ribosomal DNA loci. Genetic variation is extensive in these barley groups, and the amount of genetic diversity in cultivated barley of this region is comparable with that of cultivated barley worldwide. The level of genetic variation of HA is significantly lower than the other two barley groups, and there is also substantial heterogeneity in the level of polymorphism among different agrigeographical subregions. However, little genetic differentiation was detected among the three barley groups (HV, HA, and HS), as well as among different agrigeographical subregions. Comparison of the results from this and previous studies indicated a strong differentiation between Oriental and Occidental barley, thus favoring the hypothesis of a diphyletic origin of cultivated barley.Key words: Hordeum, allozyme, rDNA spacer-length variation, centre of diversity, phylogeny.