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dc.contributor.advisorVan Deventer, C. S.
dc.contributor.authorJacobs, Albertus Stefanus
dc.date.accessioned2018-05-17T07:36:27Z
dc.date.available2018-05-17T07:36:27Z
dc.date.issued1999-05
dc.identifier.urihttp://hdl.handle.net/11660/8282
dc.description.abstractEnglish: In South Africa nearly 47062 ha of wheat has been damaged by frost over the last ten years. This led to an average loss of income close to R 6.7 million annually. The objective of this study was to screen South African wheat cultivars for tolerance to freezing, to study the genetic variability for tolerance to freezing and to study the use of HMW-proteins to screen for tolerance to freezing. An artificial freezing test was used to screen 24 South African wheat cultivars for tolerance to freezing. Tolerance to freezing was obtained by calculating the percentage survival, root length and leaf length at -6 and -12°C. Norstar displayed superior tolerance to freezing at -6 and -12°C. Norstar, Scheepers 69, Belinda, Kavkaz, Molen, Carolus, Jager and PAN 3232 exhibited a high level of tolerance to freezing. The leaves of Caledon, PAN 3232, SST 966, SST 936, Norstar, Tugela DN and PAN 3235 showed a high level of tolerance to freezing. The roots of Kavkaz, Norstar, PAN 3235, Belinda, Jager, Carolus, PAN 3232, Betta and Molen exhibited a high level of tolerance to freezing. A full 6X6 diallel cross was used to determine the genetic variability, combining ability and inheritance of tolerance to freezing. Norstar, Tugela DN, PAN 3349, Karee, SST 66 and Snack were used as parents. Griffing's Model1, Method 1 was used for the analysis. Significant differences in tolerance to freezing were displayed by the F1- hybrids. Crosses such as SnacklNorstar, PAN 3349/Snack and Snack/fugela DN had a low level of tolerance to freezing. Karee/Norstar, SST 66/PAN 3349, Karee/PAN 3349 and SST 66/Norstar were nearly as freezing tolerant as Norstar. The lack of significant differences in the freezing tolerance between reciprocal crosses indicated that freezing tolerance was not affected by cytoplasmic effects. Norstar and Karee had the highest general combining ability. The high GCA:SCA ratio for percentage survival at -12°C and percentage reduction in survival, confirmed the additive gene action of tolerance to freezing. The high heritability estimates for percentage survival (88.18%) and leaf length at -12°C (88.45%) confirmed that tolerance to freezing is a highly heritable character. Selection for freezing tolerance in a breeding programme will be effective. The effect of HMW-proteins to screen for tolerance to freezing was studied using SOS-PAGE. Six wheat cultivars were included, Norstar, Tugela DN, PAN 3349, Karee, SST 66 and Snack. The results confirmed that HMW-proteins in coleoptiles can be used to screen for tolerance to freezing. Accumulation of the 48 kDa protein in Norstar started after the vernalisation requirement was satisfied. The 46 kDa protein is a cold sensitive protein as production stopped during cold acclimation. The 40 kDa band indicated a lack of tolerance to low temperatures. Cold tolerant cultivars were able to accumulate the 25 kDa protein rapidly when they needed protection against low temperatures. Similar reactions to cold hardening were found in the roots of the different cultivars. Snack lost the ability to produce the 68 kDa protein during prolonged periods of low temperatures. Norstar, however, was able to accumulate it during extended cold periods. All the cultivars were able to accumulate the 21, 25 and 30 kDa protein in reaction to cold hardening. The accumulation was activated once vernalisation was completed. The 19 kDa protein acted as an early defence mechanism against low temperatures. Production and accumulation of several proteins can be associated with increased tolerance to freezing. Growth habit and vernalisation requirement did influence the production and accumulation of certain HMW-proteins. A signifficant correlation between the leaf length and the number of HMW-protein bands produced was observed. This indicated that cold hardening did have an effect on the production and accumulation of HMW-proteins in coleoptiles and roots.en_ZA
dc.description.abstractAfrikaans: In Suid Afrika is daar oor die laaste tien jaar sowat 47062 ha koring beskadig deur koue, wat gelei het tot enjaarlikse verlies aan inkomste van sowat R6.7 miljoen. Die doel van hierdie studie was om die vriestoleransie van Suid Afrikaanse koringcultivars te toets, om die genetiese variasie ten opsigte van vriestoleransie te bestudeer en om hoë molekulêre gewig proteïne (HMG-proteïne) te gebruik as aanduiding van vriestoleransie. en Kunsmatige vriestoets is gebruik om die vriestoleransie van 24 Suid Afrikaanse koringcultivars te toets. Die vriestoleransie is bepaal deur die persentasie oorlewing, blaarlengtes en wortellengtes by -6 en -12°C. Norstar het die hoogste vlak van vriestoleransie by -6 en -12°C gehad. Scheepers 69, Belinda, Kavkaz, Molen, Carolus, Jager en PAN 3232 het ook hoë vlakke van vriestoleransie getoon. Die blare van Caledon, PAN 3232, SST 966, SST 936, Norstar, Tugela DN en PAN 3235 het die hoogste vlakke van vriestoleransie getoon. Die wortels van Kavkaz, Norstar, PAN 3235, Belinda, Jager, Carolus, PAN 3232, Betta en Molen het die hoogste vlakke van vriestoleransie getoon. In 6X6 dialeel is gebruik on die genetiese variasie, kombineervermoë en oorerflikheid van vriestoleransie te bepaal. Norstar, Tugela DN, PAN 3349, Karee, SST 66 en Snack is gebruik as kruisingsouers. Betekenisvolle verskille is gevind tussen die F1-basters vir oorlewing, blaarlengte en wortellengte. SnacklNorstar, PAN 3349/Snack en Snack/Tugela DN het In lae vlak van vriestoleransie getoon. Karee/Norstar, SST 66/PAN 3349, Karee/PAN 3349 en SST 66/Norstar was amper net so vriestolerant soos Norstar. Geen betekenisvolle verskille tussen kruisings en hulle resiproke is waargeneem nie, dit bevestig dat daar geen sitoplasmiese invloede betrokke was by vriestoleransie nie. Norstar en Karee het die beste algemene kombineervermoë gehad. Die hoë verhouding van algemene kombineervermoë tot spesifieke kombineervermoë bevestig die additiewe geen aksie van vriestoleransie. Die hoë oorerflikheidssyters vir persentasie oorlewing (88.18%) en blaarlengte by -12°C (88.45) bevestig die hoë oorerflikheid van vriestoleransie. Elektroforese van hoë molekulêre gewigproteïene is gebruik om die vriestoleransie van koring te toets. Ses koringcultivars is ingesluit in die proef, naamlik Norstar, Tugela DN, PAN 3349, Karee, SST 66 en Snack. Die resultate het bevestig dat hoë molekulêre gewigproteïene teenwoordig in koleoptiele van koring wel gebruik kan word om te toets vir vriestoleransie. In 48kDa proteïen het in die koleoptiele van Norstar begin opbou nadat die vernalisasiebehoefte bevredig is. Die 46 kDa proteïen is In kouesensitiewe proteïn waarvan die produksie gestaak is tydens blootstelling aan lae temperature. Die 40 kDa proteïen band was 'n aanduiding van die afwesigheid van vriestoleransie. Kouetolerante cultivars was in staat om die 25 kDa proteïen vinnig te produseer wanneer die behoefte vir beskerming teen koue onstaan het. Soortgelyke reaksies is gevind toe die hoë molekulêre gewigproteïne in die wortels ondersoek is. Onder lae temperature was Snack nie instaat om die 68 kDa proteïen vir lang periodes te produseer nie. Norstar kon die proteien egter vir lang periodes produseer wat die cultivar bestand gemaak het teen lae temperature. AI die cultivars was in staat om die 21,25 en 30 kDa proteïene te produseer. Die produksie van die proteïen is begin nadat die cultivars se onderskeie vernalisasiebehoeftes bevredig is. Die 19 kDa proteïen het opgetree as 'n vroeë beskermings meganisme. Die produksie van verskeie HMG-proteïene kan geassosieer, word met vriestoleransie. Die groeiperiode en vernalisasie behoefte van cultivars het In invloed gehad op die produksie van hierdie HMG-proteïene. 'N Betekenisvolle korrelasie tussen blaarlengte en die aantal HMG-proteïen bande geproduseer dui daarop dat koue wel In invloed het op die produksie van HMG-proteïene.en_ZA
dc.description.sponsorshipPANNAR Board of Directorsen_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectTolerance to freezingen_ZA
dc.subjectArtificial freezingen_ZA
dc.subjectSurvivalen_ZA
dc.subjectLeaf lengthen_ZA
dc.subjectRoot lengthen_ZA
dc.subjectVariabilityen_ZA
dc.subjectCombining abilityen_ZA
dc.subjectInheritanceen_ZA
dc.subjectElectrophoresisen_ZA
dc.subjectHigh molecular weight proteinsen_ZA
dc.subjectCold-tolerant plants -- South Africaen_ZA
dc.subjectWheat -- Breeding -- South Africaen_ZA
dc.subjectThesis (Ph.D. (Plant Breeding))--University of the Free State, 1999en_ZA
dc.titleGenetic variability of tolerance to freezing in South African wheat cultivarsen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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