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Accueil du site → Doctorat → Australie → 2007 → GENETIC DIVERSITY AND VARIABILITY IN GRAIN QUALITY OF SORGHUM (Sorghum bicolor (L.) Moench) LANDRACES FROM NORTHEASTERN ETHIOPIA

University of Queensland (2007)

GENETIC DIVERSITY AND VARIABILITY IN GRAIN QUALITY OF SORGHUM (Sorghum bicolor (L.) Moench) LANDRACES FROM NORTHEASTERN ETHIOPIA

Desmae, Hailemichael

Titre : GENETIC DIVERSITY AND VARIABILITY IN GRAIN QUALITY OF SORGHUM (Sorghum bicolor (L.) Moench) LANDRACES FROM NORTHEASTERN ETHIOPIA

Auteur : Desmae, Hailemichael

Université de soutenance : University of Queensland

Grade : Doctor of Philosophy (Ph.D.) 2007

Résumé
Plant genetic resources are invaluable inputs for sustaining and improving agricultural productivity. The collection and conservation of genetic diversity of important food crops has been given significant focus due to concerns over loss of genetic resources. Characterization of available diversity and chronological monitoring of the population conserved is important to understand the dynamics of genetic resources. The main aim of the present study was to assess the extent and structure of variability in sorghum landraces from North Eastern Ethiopia, and investigate the changes in variability over years. The extent and structure of variability in sorghum landraces obtained from IBC and farmers fields was assessed using morphological, SSR and ISSR markers. A wide range of variability was observed, and the analysis of variance showed significant differences in both among landraces and among geographic domains for all quantitative traits. The distribution of phenotypic classes of qualitative traits showed that non-juicy types (92%), awns at maturity (67%), white midrib color (72%), grey and straw glume color (63%), semi-compact to compact head types (68%), mostly starchy and completely starchy (82%), and 25% grain covered with glume (90%) characterize the majority of landraces. White, red, light red, straw, yellow, and brown seed colors were important accounting for more than 81% of the landraces. The Shannon-Weaver diversity index for qualitative traits ranged from 0.30 to 0.93 (mean = 0.67) for grain covering and grain color, respectively. All seven SSR primer pairs generated high levels of polymorphism, and a total of 106 alleles (15.1 alleles per locus) were observed across the landraces. The gene diversity for the entire landraces ranged from 0.52 (sbKAFGK-I) to 0.85 (sb4-32) with mean 0.72. For ISSRs, a high number of bands ranging from 34 to 87 were generated with 162 bands in total. The gene diversity ranged from 0.82 (FISSR 6) to 0.90 (FISSR 2 and 7). Cluster analyses showed no distinct pattern in the clustering of landraces based on geographic origin. The differentiation of landraces among geographic domains based on qualitative traits appeared to be weak where 97% and 95% of the variation was accounted for by within zone and altitude variation, respectively. Relatively higher differentiation (14%) was observed between districts. Similarly, no strong genetic differentiation among landraces was observed between the different geographical domains based on SSR markers. Comparison of the morphological and molecular marker systems showed that the similarity coefficients were substantially different, with SSRs displaying the lowest similarity value (0.19) while similarity in terms of qualitative traits was relatively high (0.49). No strong correlation was observed between similarity matrices, and the clustering of the landraces was different for the different marker systems. A farm survey was performed, and morphological and molecular evaluations of landraces collected in 1973 and 2003 were performed to understand the trend of the landraces variability over years. Preliminary analysis of the farm survey indicates that some important landraces have disappeared either locally or regionally in the past 30 years and many other landraces have become marginalized. Landraces which are less preferred in terms of agronomic value and end-use and some new introductions have become increasingly important. Farmers have become more risk averse, and factors such as declining soil fertility, more frequent drought and unreliable rainfall, and increased pest infestation have contributed to a change in farmer landrace selection. The field evaluation showed significant variability between the two collections for quantitative traits. For example, the landraces from the 1973 collection were late maturing compared to the 2003 collection. Little difference was, however, observed in overall variability in terms of both morphological and molecular diversity indices. Some alleles have been lost over years, but new alleles were also gained at the same time. The cloning and characterization of opaque-2 gene has been discussed in relation to available resources. High homologies were observed for nucleotide and protein sequences from the data base. Expression analysis revealed substantial differences among sorghum landraces. Protein and starch analyses for selected landraces and their starch gelatinization behaviour displayed substantial differences. Over all, the present study confirmed the presence of appreciable variability among sorghum landraces from North Eastern Ethiopia. Both the morphological and molecular diversity analyses as well as the protein and starch analysis revealed high variability. The importance of this variability and implications for conservation are discussed ; and suggestions are made

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