The characterisation of South African and Ethiopian bread and durum wheat cultivars for drought stress tolerance

English: Drought is a multidimensional problem in all crop species and affects large areas throughout the world. In developing countries nearly 32% of the 99 million hectare of wheat has been affected by varying levels of drought stress. The objective of this study was to characterize wheat lines and cultivars for drought tolerance using different screening methods. A greenhouse experiment was conducted to screen 54 bread wheat genotypes for tolerance to drought. The genotypes were characterized by measuring their yield and yield components. Significant varietal differences were found in all measured characteristics. T4, Bdl-36and Bdl-47 were found to be tolerant, whereas Bdl-16 and Bdl-8 were sensitive to drought stress. Grain yield was correlated positively and significantly with all measured characteristics. The correlation of grain yield with SKM and KN per spike was found to be very high. Hence, breeding for moisture stress needs the consideration of most yield components for improving the final yield. A wooden box study was also undertaken to examine the effects of moisture stress on survival and recovery percentage of 10 bread and 10 durum wheat lines and cultivars at the seedling stage. The results showed that highly significant variations were found in both the survival and recovery percentage of bread wheat genotypes and dururn wheat cultivars. Israel and Et-13 were relatively tolerant whereas Bdl-16, Bdl-8 and Bdl-41 were the most sensitive. Among durum wheat genotypes Cocorit-71, Fetan, Tob-66 and Gerardo were found to be tolerant whereas Cadu-17 and LD-357 showed sensitivity to moisture stress at the seedling stage. The bread and durum genotypes were also tested with three laboratory-screening methods for drought tolerance. They were proline accumulation, cell membrane stability and 2,3,5- triphenyl tetrazolium chloride reductions. The effect of drought stress on the accumulation of free proline in leaves of the genotypes was tested. The result showed that proline levels increased in drought stress treatment compare to the control in the majority of bread and durum wheat genotypes. The results on cell membrane stability also showed that there was significant variation among bread and durum wheat genotypes. Among bread wheat entries, Israel and Et-13 showed a low level of injury whereas Bdl-8 and Dereselign had a relatively high level of injury when they were exposed to simulated osmotic stress. Similarly, among the durum cultivars Tob-66 and Boohai showed a low level of injury and Cocorit-71 and Foka had a high level of injury. The results on cell viability by using TTC assay showed that among the bread wheat genotypes significant levels of variation were found. Although the results of the three laboratory techniques seem to be promismg m discriminating the cultivars and lines tested, further extensive field screening is required to confirm the results obtained in this study. An experiment was also carried out to determine the genetic distances between 20 selected bread wheat lines and cultivars for parental selection suited for breeding drought tolerance. The gliadin banding patterns of the lines and cultivars were screened using SDS-PAGE. The results of the study showed that the genetic distances among the entries tested were relatively small. The use of a large number of entries with a broad genetic background might be important to identify suitable parents for breeding drought tolerance.