Abstract:
Durum wheat is among the major cereal crops in Ethiopia, but its production has been challenged by several factors. Loss of diversity due to genetic erosion, drought stress and lack of stable genotypes due to genotypes by environment interactions have been among the factors that could be mentioned The overall objective of the present study was to estimate genetic erosion, drought stress and genotype by environment interaction on durum wheat. Three approaches; namely: direct observation; survey and group discussions were held to estimate genetic erosion and identify its causes in three districts of the central highlands of Ethiopia. Based on direct observation, the loss of genotypes was found to be in Dukem-Akaki (87.5%) followed by Lume (80%) and Gimbichu (60%) districts. Similarly, based on the information from the famers interviewed, the loss of diversity in the study districts was estimated to be 100 % in Ada district, where all farmers’ and old improved durum wheat varieties were lost followed by Lume (93.3%) and Gimbichu (66.7%). Field experiment for the evaluation of 64 durum wheat genotypes obtained from both landrace collections and international sources was conducted in two replications on sandy clay soil (Andoslos) at Debre-Zeit Agricultural Research Center in the 2016 main growing season. Terminal drought had highly significant effect on grain yield per plot, above-ground biomass, spike length, days to heading and grain filling period. Normalized Difference Vegetative Index(NDVI) as a stay green trait at different growth stage was significantly different among genotypes in both sandy clay and clay soils. The results suggested that genotype 63 scored the maximum NDVI value (0.84) at booting stage, in both light textured and black clay soils and started to decline from this onwards. Generally, NDVI allowed identification of better yielding lines. Screening and evaluation of xxii 144 durum wheat genotypes comprising selected landrace collections, global durum wheat collections and released durum wheat cultivars were carried out in two replications on light textured soils at Debre-Zeit Agricultural Research Center in the 2017 dry season under stress and non-stress conditions. Screening and identification of durum wheat genotypes using indices and morpho-agronomic traits were performed. The results of the combined analysis of variance showed that moisture, genotypes and their interaction had highly significant (p≤0.01) effects on grain yield. Significant and positive phenotypic and genotypic correlation coefficients were found between grain yield under low moisture stress condition with indices DRI, REI, GMP, MP and STI, suggesting that these indices would enable identify drought tolerant genotypes. Durum wheat genotypes showed variations in all the traits, except days to heading and anthesis under stressed and non-stressed. Drought stress reduced grain yield (48.3%), grain filling period (41.7%), and grain weight per spike (29.6%), 1000-grain weight (18.3%), and number of kernels per spike (16.3%). The correlation of grain filling with grain yield was strongly positive and highly significant under moisture stress (0.83)than under non-moisture stress (0.41) condition, indicating that indirect selection for improving grain yield through this trait would be effective under terminal moisture stress environment. Thousand kernel weight, kernel number, above ground biomass, harvest index, kernel number per spikelet and grain weight per spike had similar trend and they were positively and significantly correlated with grain yield under both moisture stress and non-moisture stress conditions. Based on the finding of the study, the best drought tolerant genotypes under moisture stress environment were genotypes 31 and 30 with yield reduction of 23.9% and 38.6%, respectively. Six genotypes (55, 30, 31, 91, 15 and 58) were found among the top 10% high yielding genotypes, and showed superior performance under both drought stress as well as well-watered non-moisture stress conditions. Genotype by environment interactions and stability analysis for 25 drought tolerant durum wheat genotypes were performed for grain yield, yield related traits and protein content in the 2017 main season. The combined analysis of variance indicated highly significant effects of genotypes, environments and their interactions on grain protein content, grain yield and yield related traits, except spike length and number of spikelets per spike which in that order showed no effects due to environment and environment by genotype interaction. The largest variation in grain protein was accounted for by environments (81.1%), followed by GEI (13.6 %) and then genotypes (5.3%). xxiii Similarly, the largest variation in grain yield was accounted for by environments (60.6%), followed by GEI (20.6%) and then genotypes (18.2%). The stability analysis using parametric measures identified G-24 as the most stable genotype followed by G-23 with above average grain yield.