Genetic variability and breeding potential of barley (Hordeum vulgare L) landraces from north Shewa in Ethiopia

English: Genetic variability and breeding potential of barley landraces from north Shewa in Ethiopia was studied with the aims i) to generate information about the level of diversity within and among the landraces in terms of morphological descriptors, SDSPAGE of seed storage proteins, and Amplified Fragment Length Polymorphism (AFLP) ii) to assess yield relationships and expected genetic advance that may be achieved through selection within or among landraces iii) to estimate genetic variances for agronomic characters from crosses involving selected barley landrace lines and predict the breeding potential of landraces and iv) to prove genetic differences between landraces, claimed by farmers, in response to waterlogging stress. The phenotypic diversity of 44 landraces, including farmers' cultivars, was estimated using Shannon Weaver diversity index for different qualitative an~ quantitative characters. This was further supplemented with SDS-PAGE of seed storage proteins and the two measures of variability were compared. Of the 44 landraces, emphasis was given to farmers' cultivars from which five to six pure line derivations from them were evaluated under field conditions to assess potential differences for agronomic characters and to estimate genetic advance that may be achieved through selection within the cultivars. Variability between lines within the cultivars for the quantitative characters was further assessed with the help of SDS-PAGE. Diallel crossing between five selected landrace lines differing in agronomic characters was carried out and genetic parameters and breeding potential of the parents were estimated. Three of the parents used for crossing were further investigated for their differences in growth and nutrient accumulation under waterlogging stress in a greenhouse pot experiment. Both morphological and SDS-PAGE data demonstrated the variability existing in the landraces. H'values pooled over morphological characters ranged from 0.12±0.08 to 0.57±0.11. Among the qualitative characters, landraces showed higher levels of polymorphism for spike type than for kernel colour, spike density and caryopsis type (covered or naked). Caryopsis type was the least diverse character observed. Diversity for quantitative characters pooled over landraces was generally very high especially for number of seeds spike" and days to maturity with respective H' values of 0.90 and 0.98. SDS-PAGE data based on representative lines from each landrace showed very low to high within landrace variability. Lines from landraces differed from each other in number and migration distances of bands. Some landraces that looked uniform for spike morphology also showed differences in banding patterns. It was also observed that some landraces displaying different spike characters, and hence assumed to exhibit differences of comparable magnitude in storage protein variability, did not reveal much differences. Variability between landraces was higher than within landraces and variability within farmers' cultivars was lower than within accessions. Clustering results of landraces from SDS-PAGE data were different in composition from those formed by morphological characters. Clustering from morphological data highlighted distinct grouping of landraces based on similarities in morphological characters whereas SDSPAGE data did not depict such distinctness. AFLP analysis of the genetic relationships between farmers' cultivars using six primer combinations illustrated varying degrees of genetic dissimilarity (0.372 to 0.728) with a mean of 0.545. Thirty one percent of the values in this range were 0.500 while 69 % of the values were > 0.600 demonstrating the presence of sufficient variation between the farmers' cultivars. The number of scoreable fragments amplified by each AFLP primer combination varied from 49 to 118 with an average of 84.5 and polymorphic fragments for each primer combination varied from 27 to 77 the average being 58.5. The average percent polymorphism was 69.9 % with values ranging from 55.1 % to 75.8%. Field evaluation of pure lines from farmers' cultivars indicated that genetic gain through selection for yield and yield components within the farmers' cultivars from this particular environment is minimal. Selection may even end up with negative gain unless carefully carried out to isolate those that might be useful to bring slight improvement in yield. Carefully excluding the inferior types to upgrade yield potential is suggested rather than attempting to improve them through extensive pure line selection and evaluation methods. Evaluation of landraces from other sources, from within or outside this parrticular environment, is suggested to get better yielding landraces than the existing ones. In the long term, crossing may be scheduled between cultivars which, based on morphological characters and protein profiles, appear to be diverse in order to maximize the potential gain from selection in the progeny. Estimated genetic parameters from diallel crosses of barley landrace lines highlighted the importance of additive gene actions for spike length, number of seeds spike¹ and grain yield spike¹under free drainage conditions and for days to heading and days to maturity at both treatment levels. Both additive and non-additive gene actions were important in the control of grain yield under free drainage conditions. By contrast, estimates of genetic parameters for yield and yield components (except spike length) were very low or negative under waterlogged conditions. Among the parents, Feres Gama(37) and 1153(28) contributed the highest positive GCA effects and comparable SCA variances for yield and yield components under free drainage conditions. Hence, these parents shall be tested thoroughly in order that maximum use of their superior combining ability can be made in future crossing programs for environments free of waterlogging stress. A separate crossing and selection program is suggested for the respective environmental conditions if resources permit. Waterlogging reduced the total number of tillers per pot of the tolerant landrace Mage(07) and Feleme(68) by 43 % and 48 %, respectively compared to the control plants while it was only 23 % for the susceptible landrace Feres Gama(37). Total shoot dry matter accumulation under waterlogged conditions was comparable for all three landraces in spite of the largest number of tillers produced by Feres Gama(37). Differences between the susceptible and tolerant landraces in response to waterlogging were largely due to less dry matter accumulation of the tillers and slower growth in the susceptible landraces. Moreover, apparent differences were noticed in P concentration and uptake between the tolerant and susceptible landraces, the effect being less for the tolerant landrace Mage(07) than for the susceptible landrace Feres Gama(37). Difference in N concentration of shoots between Feres Gama(37) and Mage(07) was also observed although the magnitude was not comparable to that of P.