Submitted to: Plant Genetic Resources: Characterization and Utilization
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2005
Publication Date: 7/1/2006
Citation: Jaradat, A.A., Shahid, M. 2006. Population and multilocus isozyme structures in a barley landrace. Plant Genetic Resources: Characterization and Utilization. 4(2):108-116. Interpretive Summary: Traditional farmers in the marginal regions and stress-prone environments of Oman have maintained a wealth of intra-specific variation of the salt-tolerant Batini barley landrace. Understanding the relationships among and within populations of this landrace has important implications in the design of programs for the conservation of its genetic diversity. Total population diversity and its components were estimated on the basis of 10 isozymes scored on 450 single plants representing seven subpopulations. Subpopulations contributed to total diversity either through high intra- or high inter-population diversity. Isozyme markers showed a wide range of fixation and high levels of diversity and multilocus associations; these associations were not independently distributed in subpopulations. Average genetic identity and genetic distance between subpopulations confirms the presence of valuable genetic diversity in this landrace. Results of the study can be utilized by germplasm collectors to maximize genetic diversity in germplasm collections and by geneticists to design on-farm conservation strategy and to help farmers maintain the high level of diversity and population differentiation in this landrace.
Technical Abstract: Isozyme data was used to assess genetic diversity within and among a subdivided population of the salt-tolerant Batini barley landrace. Total population diversity and its components were estimated on the basis of 12 isozymes scored on 450 single plants representing seven subpopulations. Of the 36 alleles observed, eight were rare, 13 were common widespread, nine were common sporadic, and six were localized. Two principal components, based on mean gene diversity (h = 0.192 ± 0.019), Shannon's diversity index (I = 0.337 ± 0.034), percent polymorphic loci (P-0.05 = 49.07 ± 7.0%), genetic identity (IN = 0.918 ± 0.023) and genetic distance (DN = 0.080 ± 0.032) among subpopulations accounted for 91.7% of total variation and separated subpopulations into four distinct groups. Contributions to total diversity (HT = 0.1925 ± 0.02) by individual subpopulations was partitioned into intra- (CS, range: -0.035 to 0.0191) and inter-population (CST, range: -0.009 to 0.0095) components. Subpopulations with high Ae, h, and low P-0.05, contributed more to the intra-population component, whereas those with high P-0.05, and low I, contributed more to the inter-population component of total diversity. Two subpopulations contributed negatively to total diversity either due to lower than average CST (Batini-3) or CS (Batini-7). A large percentage (81.53%) of total genetic diversity was apportioned among subpopulations (GST = 18.47%). Sixty-three percent of Wright's fixation indices (average FST = 0.42 ± 0.08) for isozymes were significantly higher than zero (ranged from 28.7% for Pgi-1 and Pgd-3 to 85.7% for Est-1, Est-5, Pgi-2, and Pgd-1). However, indirect estimate of gene flow (Nm = 2.33) was relatively high among subpopulations. Multilocus associations of varying order were detected for three groups of isozymes (G1 = Esterase-1, -2, -4 and -5; G2 = Aco-1, Aco-2 and Pgd-3; and G3 = Acp-3, Pgd-1, and Pgd-2). Genetic identity (IN) and minimum genetic distance (DN) among subpopulations confirm the presence of valuable genetic diversity in this landrace. Results of the study can be utilized to maximize genetic diversity in germplasm collections, and to design on-farm conservation strategy for this landrace.