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

[摘要] English: Genetic variability and breeding potential of barley landraces from north Shewa inEthiopia was studied with the aims i) to generate information about the level ofdiversity within and among the landraces in terms of morphological descriptors, SDSPAGEof seed storage proteins, and Amplified Fragment Length Polymorphism (AFLP)ii) to assess yield relationships and expected genetic advance that may be achievedthrough selection within or among landraces iii) to estimate genetic variances foragronomic characters from crosses involving selected barley landrace lines and predictthe breeding potential of landraces and iv) to prove genetic differences betweenlandraces, claimed by farmers, in response to waterlogging stress. The phenotypicdiversity of 44 landraces, including farmers' cultivars, was estimated using ShannonWeaver diversity index for different qualitative an~ quantitative characters. This wasfurther supplemented with SDS-PAGE of seed storage proteins and the two measures ofvariability were compared. Of the 44 landraces, emphasis was given to farmers'cultivars from which five to six pure line derivations from them were evaluated underfield conditions to assess potential differences for agronomic characters and to estimategenetic advance that may be achieved through selection within the cultivars. Variabilitybetween lines within the cultivars for the quantitative characters was further assessedwith the help of SDS-PAGE. Diallel crossing between five selected landrace linesdiffering in agronomic characters was carried out and genetic parameters and breedingpotential of the parents were estimated. Three of the parents used for crossing werefurther investigated for their differences in growth and nutrient accumulation underwaterlogging stress in a greenhouse pot experiment.Both morphological and SDS-PAGE data demonstrated the variability existing in thelandraces. H'values pooled over morphological characters ranged from 0.12±0.08 to0.57±0.11. Among the qualitative characters, landraces showed higher levels ofpolymorphism for spike type than for kernel colour, spike density and caryopsis type(covered or naked). Caryopsis type was the least diverse character observed. Diversityfor quantitative characters pooled over landraces was generally very high especially fornumber 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 tohigh within landrace variability. Lines from landraces differed from each other innumber and migration distances of bands. Some landraces that looked uniform for spikemorphology also showed differences in banding patterns. It was also observed thatsome landraces displaying different spike characters, and hence assumed to exhibitdifferences of comparable magnitude in storage protein variability, did not reveal muchdifferences. Variability between landraces was higher than within landraces andvariability within farmers' cultivars was lower than within accessions. Clustering resultsof landraces from SDS-PAGE data were different in composition from those formed bymorphological characters. Clustering from morphological data highlighted distinctgrouping of landraces based on similarities in morphological characters whereas SDSPAGEdata did not depict such distinctness.AFLP analysis of the genetic relationships between farmers' cultivars using six primercombinations illustrated varying degrees of genetic dissimilarity (0.372 to 0.728) with amean of 0.545. Thirty one percent of the values in this range were0.500 while 69 %of the values were > 0.600 demonstrating the presence of sufficient variation betweenthe farmers' cultivars. The number of scoreable fragments amplified by each AFLPprimer combination varied from 49 to 118 with an average of 84.5 and polymorphicfragments 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 % to75.8%.Field evaluation of pure lines from farmers' cultivars indicated that genetic gainthrough selection for yield and yield components within the farmers' cultivars from thisparticular environment is minimal. Selection may even end up with negative gain unlesscarefully carried out to isolate those that might be useful to bring slight improvement inyield. Carefully excluding the inferior types to upgrade yield potential is suggestedrather than attempting to improve them through extensive pure line selection andevaluation methods. Evaluation of landraces from other sources, from within or outsidethis parrticular environment, is suggested to get better yielding landraces than theexisting 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 tomaximize the potential gain from selection in the progeny.Estimated genetic parameters from diallel crosses of barley landrace lines highlightedthe importance of additive gene actions for spike length, number of seeds spike¹ andgrain yield spike¹under free drainage conditions and for days to heading and days tomaturity at both treatment levels. Both additive and non-additive gene actions wereimportant 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, FeresGama(37) and 1153(28) contributed the highest positive GCA effects and comparableSCA variances for yield and yield components under free drainage conditions. Hence,these parents shall be tested thoroughly in order that maximum use of their superiorcombining ability can be made in future crossing programs for environments free ofwaterlogging stress. A separate crossing and selection program is suggested for therespective environmental conditions if resources permit.Waterlogging reduced the total number of tillers per pot of the tolerant landraceMage(07) and Feleme(68) by 43 % and 48 %, respectively compared to the controlplants while it was only 23 % for the susceptible landrace Feres Gama(37). Total shootdry matter accumulation under waterlogged conditions was comparable for all threelandraces in spite of the largest number of tillers produced by Feres Gama(37).Differences between the susceptible and tolerant landraces in response to waterloggingwere largely due to less dry matter accumulation of the tillers and slower growth in thesusceptible landraces. Moreover, apparent differences were noticed in P concentrationand uptake between the tolerant and susceptible landraces, the effect being less for thetolerant landrace Mage(07) than for the susceptible landrace Feres Gama(37).Difference in N concentration of shoots between Feres Gama(37) and Mage(07) wasalso observed although the magnitude was not comparable to that of P.

[发布机构] University of the Free State