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

Abstract

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.

Afrikaans: Droogte is 'n multidimensionele probleem in alle landbou gewasse en affekteer groot areas oor die hele wêreld. In ontwikkelende lande word amper 32% van die 99 miljoen hektaar koring geaffekteer deur verskillende vlakke van droogte stres. Die doel van hierdie studie was om koring genotipes te karakteriseer vir droogte toleransie met die gebruik van verskillende evaluasie tegnieke. 'n Glashuis eksperiment is gedoen om 54 koring genotipes te evalueer vir toleransie vir droogte. Die genotipes is gekarakteriseer deur hulle opbrengs en opbrengs komponente te meet. Betekenisvolle verskille is tussen inskrywings gevind vir alle gemete eienskappe. T4, Bdl-36 en Bdl-47 was droogte tolerant terwyl Bdl-16 en Bdl-8 sensitief was vir droogte. Opbrengs was positief en betekenisvol gekorreleer met alle gemete eienskappe. Die korrelasie van graan opbrengs met SKM en KN per aar was baie hoog. Daarom moet, vir teling vir droogte toleransie, meeste opbrengs komponente in ag geneem word om die finale opbrengs te verbeter. 'n Hout kas studie is ook gedoen om die effek van droogte stres op oorlewing en herstel persentasie van lObrood en 10 durum lyne en cultivars in die saailing fase te meet. Die resultate het aangetoon dat hoogs betekenisvolle variasies gevind is vir beide oorlewing en herstel persentasie van brood en durum korings. Israel en Et-13 was relatief tolerant teen stres, terwyl Bdl-16, Bdl-8 en Bdl-41 die sensitiefste was. By die durum korings was Cocorit-71, Fetan, Tob-66 en Gerardo tolerant terwyl Cadu-17 en LD-357 sensitiefwas vir droogte stres in die saailing fase. Die brood en durum genotipes is ook met drie laboratorium prosedures getoets vir droogte toleransie. Prolien akkumulasie, sel membraan stabiliteit en 2,3,4-triphenyl tetrazolium chloried reduksie is gebruik. Die effek van droogte stres op akkumulasie van vry prolien in blare van die materiaal is getoets. Resultate het aangetoon dat prolien vlakke toegeneem het met droogte behandeling in vergelyking met die kontrole in meeste van die brood en durum korings. Die resultate van die sel membraan stabiliteit toetse het ook betekenisvolle variasie tussen brood en durum korings aangetoon. Vir die brood korings het Israel en Et-13 'n lae vlak van skade getoon terwyl Bdl-8 en Dereselign 'n relatiewe hoë vlak van skade getoon het as dit blootgestel is aan gesimuleerde osmotiese stres. Net so het die durum cultivars Tob-66 en Boohai 'n lae vlak van skade gehad, en Cocorit en Foka 'n hoë vlak van skade. Die resultate van sel lewensvatbaarheid deur gebruik van die TTC metode het aangetoon dat daar betekenisvolle variasie is tussen brood korings. Alhoewel die resultate van die drie laboratorium tegnieke belowende resultate gegee het om cultivars en lyne te diskrimineer vir droogte toleransie, sal verdere uitgebreide veld evaluasies nodig wees om die resultate te bevestig van hierdie studie. 'n Eksperiment is ook gedoen om te kyk na genetiese afstande tussen 20 geselekteerde brood genotipes vir ouer seleksie vir teling van droogte toleransie. Die gliadien band patrone van die lyne en cultivars is getoets met die gebruik van SDS-PAGE. Die resultate het aangetoon dat genetiese afstande tussen inskrywings relatief klein is. Die gebruik van 'n groot aantal inskrywings met 'n wye genetiese agtergrond kan belangrik wees om geskikte ouer materiaal te identifiseer vir die teling van lyne met droogte toleransie.