Molecular assessment of genetic diversity and population differentiation of hulless barley (Hordeum vulgare L.) landraces from the Himalayas of Nepal and its relevance for barley breeding
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The Himalayas are known as a region of domesticated barley diversification. Barley landraces from the Himalayas, particularly from the highlands of Nepal, share a significant part of the world barley germplasm resources. Due to the fact that hulless barley is widely grown in the highlands of Nepal from the East to the West along the Himalayas, it is frequently represented in Himalayan barley collections and can be considered as an important genetic resource. The Nepalese hulless barley landraces are frequently being used by the barley researchers; however, a more effective utilization of this genetic resource is hindered due to the lack of detailed information on genetic diversity and population differentiation. Furthermore, the extent of genetic relatedness of Nepalese hulless barley to the mainstream barley cultivars is not known. In the present investigation, a large set of hulless barley (Hordeum vulgare L. subsp. vulgare) landraces originally collected from the highlands of Nepal along the Annapurna and Manaslu Himalaya-range were analyzed for genetic relatedness and population differentiation using simple sequence repeats (SSRs). The 44 genome-covering barley SSRs revealed a high level of genetic diversity among the landraces (diversity index, DI=0.536). The genetic similarity based UPGMA clustering and Bayesian model based structure analysis revealed a complex genetic structure of the landraces. Eight genetically distinct populations were identified, of which 7 were further studied for diversity and differentiation.The populations were fairly differentiated (Theta=0.433, RST=0.445) accounting for >40% of the genetic variation among the populations. The pairwise population differentiation test confirmed that many of the geographic populations significantly differ from each other but that the differentiation is independent of the geographic distance (r=0.224, p>0.05). The genetic diversity estimated for all and each population separately revealed a hot spot of genetic diversity at Pisang (DI=0.559). The highlands of central Nepal, particularly valleys along the upper basin of the river Marshyangdi (Pisang and Thonje) are rich in hulless barley diversity, and landraces in this region are highly differentiated. The upper basin of Marshyangdi can be considered as origin of hulless barley diversity within the Himalayas range in central Nepal. The Nepalese hulless barley landraces are found genetically different from the Western and East Asian hulled as well as hulless cultivars. A detail analysis of frequency and distribution of SSR alleles between the Nepalese landraces and German hulled cultivars revealed several unique alleles. Furthermore, a significant difference in SSRs diversity estimated at genomic regions corresponding to chromosomes 2H and 6H was found between these two sets of barleys. The landraces showed resistance reaction to Barley mild mosaic virus (BaMMV) and powdery mildew (Blumeria graminis f. sp. hordei, Race D 12/12 and Race 178). However, a high degree of susceptibility was observed for leaf rust (Puccinia hordei, Race J 80). The preliminary genetic analysis indicated that diversity exists for genes conferring resistance to BaMMV, and powdery mildew in Nepalese hulless barley germplasm. The Nepalese hulless barley can be considered as an important genetic resource for mainstream barley breeding, particularly for spring types. This will broaden the genetic base of the present barley gene pool and provide novel alleles to the mainstream barley cultivars. The hulless barley populations can be used in genetic mapping to complement existing maps or for association studies to localize complex traits of agronomic importance. The small, isolated local populations like that have been described for Nepalese hulless barley germplasm can be more effective for an association study than large cosmopolitan populations.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Göttingen : http://www.cuvillier-verlag.de: Cuvillier; 2007