Genetic diversity and grain protein composition of tetraploid wheat (Triticum durum Desf) germplasm from Ethiopia
Abstract: The extent and patterns of genetic diversity in landraces of tetraploid wheat germplasm collected from major wheat-producing regions of Ethiopia were assessed with the use of agromorphological,phenol-qualitative traits, grain proteins and molecular markers. The extent of genetic erosion of landraces in tetraploid wheat germplasm from Ethiopia was also evaluated. Field evaluation of agro-morphological characters and laboratory analysis of grain proteins and molecular markers (ISSR) revealed the presence of broad genetic variation among accessions grown in different regions of Ethiopia. Based on the agro-morphological traits, all accessions included in the study were clustered into 15 clusters, with nine accessions remaining solitary. The first 5, 4 and 3 principal component analyses were involved in explaining most of the variation between region of origin, species and altitudinal classes, respectively. Biomass yield per plot, nature of awn, days to heading, lower glume shoulder width, kernel (seed) colour and stand count at emergence were consistently important in explaining the variation in all accessions studied across region of origin, species and altitude class. Of the phenologic and qualitative traits evaluated in all accessions across the region of origin, the highest Shannon-Weaver diversity index (H′) was mainly due to plant height, a major agronomic character in durum wheat, except for landraces from Arsi and Bale, where it was due to awn colour. Characterisation of Ethiopian tetraploid wheat germplasm for glutenin sub-unit composition resulted in identification of novel alleles at the Glu-1 locus. About 39% of the durum wheat studied contained Glu-A1x sub-units, which are rare in other durum wheats.Although there is monomorphism in a number of accessions for gliadin and glutenin subunits, in this study the B genome was found to be more polymorphic than the A genome. Analysis of DNA polymorphism with ISSR primers produced 128 polymorphic bands and allowed a separation of 60 accessions of tetraploid wheat genotypes. The Nei genetic distance for all accessions varied from 0.0090 to 0.8574 and that for region of origin from 0.045 to 0.138. Molecular characterisation of four species of Triticum using ISSR revealed that these species were clearly separated, with T. durum being the most diverse, followed by T. turgidum, T. aethiopicum and T. dicoccon in that order. Triticum durum was more closely related to T.turgidum than to the other species. The broad diversity in tetraploid Ethiopian wheat germplasm demonstrated here can be utilised in genetic improvement of the crop through selection and hybridisation. However, this broad genetic diversity is being threatened by genetic erosion. For conservation and practical application reasons, it is necessary to embark on more comprehensive and systematic germplasm collection from all over Ethiopia, with ex situ conservation and appropriate in situ conservation at the site of origin of landraces. This would also help to prevent genetic erosion arising from landraces being replaced by improved varieties of hexaploid and/or tetraploid wheat.
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