GENETIC DIVERSITY AND MARKER TRAIT ASSOCIATIONS IN BARLEY (Hordeum vulgare L.) LANDRACES OF ETHIOPIA FOR ADAPTATION TO ACIDIC SOILS

Abstract

Barley is an indispensable food security as well as potential industrial crop in Ethiopia. Its importance is remarkable in the daily life among various societies in the vast highland of the country. Despite the significance of dietary and malt importance of barley, its productivity is far below attainable potential which is attributed to various biotic and abiotic factors, of which soil acidity is one of the major production constraints. Therefore, development of improved barley varieties with high yield potential and adaptable to the stress environments particularly acid soil is an indispensable priority in the country. Thus, in the present study seven interlinked field and laboratory experiments were conducted. The general objective of the experiment was to identify barley genotypes for yield potential, acid soil tolerance, and grain nutrient rich genotypes to enhance sustainable production and yield stability in the country. The first two experiments were conducted using 320 barley genotypes using alpha lattice design with two replications at Holeta, Jeldu and Midakegn during 2017 and 2018, to study genetic diversity and variability, to assess morpho agronomic traits association, to estimate heritability, genetic advance and to identify acid soil tolerant barley genotypes. Accordingly, field screening experiment revealed that significant (P≤ 0.001) differences among the genotypes and genotypes by environment interaction was detected for most of the traits indicating adequate variability under both lime treated and acidic soil conditions. Based on multiple traits cluster analysis, barley genotypes were grouped into five distinct clusters with significant distance indicating adequate diversity between some of the clusters while, populations from different regions of collection were grouped to four clusters. Moreover, significant positive association among different traits and between grain yield and the other morpho-agronomic traits was observed indicating potential opportunity for simultaneously improving these attributes. Likewise, heritability of the traits ranging from 58% to 97% and 58% to 94%; genetic advance from 6.3% to 67.3% and 7.4% to 76.8% under non-stress and stress soil conditions respectively. The first and second principal components of yield and stress indices accounted for 99.3% of total variability suggesting that the two components adequately explained the variation in the data. Moreover, grain yield under stress showed strong positive correlation with yield under non-stress (r = 0.89**). xxiv Besides, Stess Tolerance Index (STI), Geometric Mean Productivity (GMP), Mean Productivity (MP), Aluminum Adaption Index (AAI) and Aluminum Tolerance Index (ATI) revealed the existence of strong positive correlation among indices and with yield performance under both soil environments. The third experiment focused on the molecular genetic diversity and genome wide association study in Ethiopian barley landraces using SNP markers. The study was designed to determine genetic diversity, the population structure and marker trait association in 283 barley study panels to identify markers associated with various agro-morphological traits and acid soil stress tolerance indices. Barley populations evaluated were grouped into three genetic sub populations. Analysis of molecular variance revealed the presence of high genetic variation (93 %) within the population than between the regions (7%) with moderate or low genetic differentiation coefficient (PhiRT = 0.073) and high gene flow (Nm = 6.4). Moreover, GWAS were carried out using phenotypic traits and 28902 SNP markers with PCs and kinship matrix in MLM. A total of 976 significant (P ≤ 0.0001) marker trait associations for the traits studied were detected explaining 4 to 28% phenotypic variation under both soil conditions. Similarly, associations of SNP markers and stress indices also showed 312 marker trait association explaining 4 to 14% of phenotypic variation. The current study advances our understanding about the genomic loci associated with key agronomic traits and acid soil tolerance indices in barley, and calls for their further exploration and validation to initiate marker development for subsequent marker assisted breeding. Analysis of genetic variability and association among grain quality attributes revealed significant (P ≤ 0.01) differences among the genotypes indicating good scope for improvement. Genotypic means of element content combined across the acid soil stress and non-stress showed that Fe content ranged from 40.1 to 83.9 mg kg-1 , Zn from 17.9 to 41.8 mg kg-1 , Ca from 308.5 to 500.7 mg kg-1 , P from 1616.5 to 3168.0 mg kg-1 , K from 3762.7 to 6608.3 mg kg-1 , CA from 1.6 to 2.4 %. Likewise, CP content ranged from 9.3 to 14.8%, HLW from 54.2 to 77.3 kg hl-1 and TKW from 31.5 to 60.9g. Broad-sense heritability (h2 ) estimated were within the range of 86.9% to 94.6% for Fe, Zn, K, Ca, CA, CP, HLW and TKW. These results signify good prospects of barley landraces for improvement of grain quality trait of interest via bio-fortification in the future. Seedling root and shoot growth performance evaluation under both soil condition was executed using soil bioassay to investigate genetic variability and association with grain yield performance. Analysis of variance revealed significant (P≤ 0.001) difference among genotypes for root and shoot growth traits and acid soil tolerance indices indicating substantial variability among barley genotypes. Correlation between xxv different root growth attributes and grain yield under acidic soil condition revealed significant positive (P≤ 0.05) association. Root length in acid soil pot trial could be used for fast-track indirect selection trait in early generation testing of large genotype. Therefore, the currently identified acid soil tolerant and high yielding genotypes should be utilized for further adaptation study and simultaneous parental line development. Furthermore, farmers’ participatory field experiment was conducted with the objectives to study yield performance of selected thirty barley genotypes under contrasting acid soil condition and to understand farmers’ preference in participatory barley variety evaluation. Significant (P≤ 0.01) positive association was observed among selection score of farmers and breeders under field evaluation as well as post-harvest grain assessment. Besides, grain yield under limed versus yield under acid soil revealed significant positive correlation (r= 0.61) and grain yield versus selection scores also disclosed significant positive association. The last activity was to study G × E interaction and stability analysis using thirty barley genotypes across nine test environments. AMMI analysis of variance for grain yield showed highly significant (P≤ 0.001) differences due to genotypes, environment and G×E interaction. Environment accounted for (54.61%) of the total variations followed by genotype (10.69%) and G×E interaction (34.70%). Moreover, a substantial percentage of the G×E interaction sum of squares was explained by IPCA1 (45.48%) followed by IPCA2 (24.65%) and IPCA3 (13.02%) while the first two IPCAs explained 70.13%. Moreover, AMMI and GGE were found to be efficient in grouping the barley growing environment in the central highland whereas DebreMarkos and Bekoji were good representative testing environments. This study revealed that 3514-A, 24990, 17148 including HB-1307 and Ibon174/03 were desirable genotypes for breeding line identification for subsequent crossing works. Overall, the present study recognized the potential of barley accessions for yield and related traits which could be used as sources of variability for future breeding programs to improve acid soil tolerance and nutritional qualities in barley breeding thereby increase barley productivity