Drought tolerance studies in spring wheat cultivars produced in South Africa

Strauss, Johannes Abraham (1999-12)

Thesis (Ph.D.(Agric.)) -- University of Stellenbosch, 1999.

Thesis

ENGLISH SUMMARY: Drought is considered, worldwide, to be the most important factor limiting crop yields. Spring wheat produced in the Western Cape region of South Africa is also affected by water stress. The onset of global warming may cause periods of water stress in the winter rainfall regions of South Africa more frequently, which makes it important to identify spring wheat cultivars that can withstand these conditions. The aim of this study was to determine whether cultivar differences in drought tolerance could be detected through the use of a series of physiological tests on spring wheat plants subjected to water stress at different growth stages. Furthermore to determine whether differences in physiological responses would be of any commercial value. To evaluate this, plants were analyzed to compare biomass production, yield and quality of stressed and control (unstressed) plants. A preliminary trial showed that the withholding of water might be more appropriate in the induction of water stress than the use of polyethylene glycol. The trial also showed that the reduction of 2,3,5-triphenyltetrazoliumchloride (modified method) was not sensitive enough to detect water stress in spring wheat. The evaluation of the physiological parameters showed that differences in drought tolerance do exist in spring wheat cultivars produced in the Western Cape region. The accumulation of proline and the water content of leaves proved to be the most sensitive parameters tested. A combination of these parameters may provide valuable information in newly bred spring wheat cultivars. In a study on biomass production it was shown that the above ground biomass was reduced by applied water stress. No clear distinctions in drought tolerance could, however, be made between cultivars. The use of leaf area (rate of leaf abscission) shows promise as a method to distinguish between drought tolerant cultivars. Yield and the yield components of all cultivars tested were severely reduced by water stress at both the flag leaf-, milky kernel growth stage. Although reductions in yield and yield components was shown, no single cultivar proved more tolerant than the other. The application of water stress resulted in a general increase in kernel protein content. Flour yield was lower, due to a relatively smaller production of non-protein components in the kernel. Although protein content increased with increased water stress, no significant differences were noted in micro-loaf volumes. The results of the mixograph parameters tested were also similar.

AFRIKAANSE OPSOMMING: Droogte word wereldwyd beskou as een van die belangrikste faktore wat gewasopbrengste beperk. Lentekoringkultivars wat in die Wes-Kaap streek in Suid-Afrika verbou word, word ook deur waterstremming beinvloed. Die koms van die kweekhuis-effek mag veroorsaak dat die winterreenvalgebiede van Suid- Afrika meer en meer bloogestel word aan periodes van waterstremming. Dit is dus belangrik om kultivars te identifiseer wat heirdie toestande kan weerstaan. Die doel van die studie was om te bepaal of kultivarverskille ten opsigte van droogteverdraagsaamheid in lentekoring kultivars, wat aan waterstremming tydens verskillende groeistadiums, blootgestel is, ge'identifiseer kan word. 'n Reeks fisiologiese toetse is gebruik om die bepalings te doen. Verder is die biomassa produksie, opbrengs en kwaliteit van gestremde en kontrole (geen stremming) plante ontleed om te sien of verskille in fisiologiese reaksies van enige kommersiele waarde is. Tydens 'n loodsproef is aangetoon dat die onthouding van water dalk meer geskik is as die gebruik van poli-etileen glikol om waterstremming te induseer. Verder is ook aangetoon dat die reduksie van 2,3,5- trifenieltetrazoliumchloried (aangepaste metode) nie sensitief genoeg was om waterstremming in lentekoringkultivars uit te wys nie. Die evaluering van die fisiologiese parameters het daarop gewys dat daar wei verskille in droogteverdraagsaamheid bestaan tussen lentekoring kultivars wat in die Wes-Kaap verbou word. Die ophoping van vry prolien en die waterinhoud van blare het geblyk die sensitiefste parameters te wees. 'n Kombinasie van al die getoetste parameters kan waardevolle inligting verskaf in die teel van nuwe lentekoringkultivars. In 'n studie van biomassaproduksie is aangetoon dat biomassa van lentekoring verlaag word deur waterstremming tydens die vlagblaar- en melkdeegstadium individueel en tydens beide groeistadiums gekombineerd. Geen duidelike verskille in droogteverdraagsaamheid tussen verskillende kultivars kon egter verkry word nie. Die gebruik van blaaroppervlaktebepalings toon egter belofte as 'n metodeom tussen kultivars vir droogteverdraagsaamheid te onderskei. Die opbrengs en opbrengskomponente van lentekoringkultivars is erg verlaag deur waterstremming tydens die vlagblaar-, melkdeeg- en beide groeistadiums gekombineerd. Alhoewel verlagings in die opbrengs van lentekoring gevind is, het geen kultivar beter gevaar as 'n ander opbrengs as parameter gebruik word nie. Dieindusering van waterstremming het 'n algemene verhoging van korrelprote"ien veroorsaak. Meel opbrengs is verlaag deurdat 'n verlaging in die produksie van die nie-proteien komponent van die korrels veroorsaak is. Alhoewel korrelproteien verhoog is, is geen betekenisvolle verskille in die mikro-broodvolumes of die mixogram-parameters vir die getoetste kultivars waargeneem nie.

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