Initiation of a pre-breeding effort for water stress resistance traits and yield improvement in wheat
Mthembu, Jabulani Bhekisisa (2018-12)
ENGLISH ABSTRACT: Wheat (Triticum aestivum L.) is an important crop produced in South Africa and across the world. Water stress and rust diseases (Puccinia spp.) are common factors hindering wheat growth and development. Leaf lifespan is reduced under water stress conditions from the leaf being infected by rust diseases. High-heritable Mendelianinherited and quantitative traits as well as male sterility mediated marker assisted selection (MS-MARS) technique was utilised for water stress and rust disease resistant wheat characterisation. The aim of the study was initiation of a pre-breeding effort for water stress resistance traits and yield improvement in wheat Sixty high-yielding genotypes and a female F1 1:1 male sterile and male fertile segregating population postulated to carry the leaf and stem rust resistance genes were screened for the presence of Lr34, Sr2, Sr31, Sr24, Lr37, Sr26 and Lr19 markers using a routinely standardised panel of markers used in the Stellenbosch University Plant Breeding Laboratory. Molecular characterisation of wheat lines was followed by cross-pollinations of a selected male sterile female and donor lines in the growth chamber using a reticulated hydroponic system (RHS) for the MS-MARS cycle scheme. Male fertile tillers were allowed to self-pollinate and were used for singleseed dehiscence. Sixty genotypes were phenotypically screened using identified and selected target traits associated with water stress resistance. Five genotypes were selected and further screened for water stress resistance using added traits of interest. An RHS was utilised for screening of the target traits including excised-leaf water loss, leaf relative water content, specific leaf area, number of tillers (NT), number of leaves and lengthrelated parameters such as root length (RL) and shoot length (SL). Fresh weight parameters included roots fresh weight (RFW), shoots fresh weight (SFW), leaves fresh weight (LFW) and total plant fresh weight (TPFW). Dry weight parameters included roots dry weight, shoots dry weight, leaves dry weight (LDW), above-ground dry weight and total plant dry weight (TPDW). Additional traits included chlorophyll content index (CCI), stomatal conductance, photosynthetic active radiation, leaf area index, radiation use efficiency, relative growth rate (RGR) and root-to-shoot ratio. Rust disease resistant genotypes were identified from the studied population. Molecular characterisation of the wheat genotypes for rust resistance genes showed increased allele frequencies in MS-MARS cycles 1 to 2 for both female and male lines, more specifically Lr34 and Sr2. However, the male lines showed lower allele frequencies and absence of the Lr19 marker in the population. Analysis of variance showed that water stress significantly influenced the growth and development of wheat genotypes for all the studied traits except RL and NT. The selected five genotypes showed better water stress resistance for all the traits studied. Genotypes were ranked as follows based on their performance under water stress conditions: 15HYLD-30, 15HYLD-22, 15HYLD-29, 15HYLD-18 and 15HYLD-26. A strong positive association observed under water stress conditions from fresh weight components included LFW and RFW (r = 0,884), followed by TPFW with FW components such as RFW (r = 0,848), SFW (r = 0,922) and LFW (r = 0,920). A strong positive association was also recorded for SFW and SL (r = 0,832), CCI with SL (r = 0,835) and SFW (0,890) and lastly, TPDW with RGR (r = 0,879) and LDW (r = 0,872). A strong positive association was recorded under well-watered conditions namely TPFW showed a strong positive association with SFW (r = 0,872), LFW (r = 0,920), TPDW with SL (r = 0,877) and LDW (r = 0,841).
AFRIKAANSE OPSOMMING: Koring (Triticum aestivum L.) is ŉ belangrike gewas wat in Suid-Afrika en wêreldwyd verbou word. Waterstres en roessiektes (Puccinia spp.) is algemene faktore wat die groei en ontwikkeling van koring belemmer. Blaarlewensduur word onder waterstresomstandighede verlaag deur blare wat met roessiektes besmet word. Hoë vererfbare Mendeliaanse oorgeërfde en kwantitatiewe eienskappe en die tegniek van manlike steriliteitsbemiddelde merkergeassisteerde seleksie (MS-MARS) is vir karakterisering van waterstres- en roessiekteweerstand onder koring gebruik. Die doel van die studie was die toepassing van ŉ voorkwekingspoging gemik op eienskappe van waterstresweerstand vir die verhoging van koringopbrengste. Sestig hoë-opbrengsgenotipes en vroulike F1 1:1 manlike steriele en manlike vrugbare geskeide populasies wat veronderstel is om die blaar- en stamroesweerstandgene te dra, is gesif vir die teenwoordigheid van Lr34-, Sr2-, Sr31-, Sr24-, Lr37-, Sr26- en Lr19-merkers met behulp van ŉ roetinegestandaardiseerde paneel merkers wat in die Universiteit Stellenbosch se planttelingslaboratorium (SU-PBL) gebruik word. Molekulêre karakterisering is opgevolg met kruisbestuiwings van seleksies manlike steriele en skenkerlyne in die groeikamer met gebruik van ŉ hidroponiese stelsel vir die MS-MARS-siklusskema. Manlike vrugbare waterlote is toegelaat om te selfbestuif en is gebruik vir enkelsaadoopspringing. Sestig genotipes is fenotipies gesif met gebruik van geïdentifiseerde en gekose teikeneienskappe wat met waterstresweerstand geassosieer word. Vyf genotipes is gekies en verder gesif vir waterstresweerstand met behulp van bykomende belangwekkende eienskappe. ŉ Geretikuleerde hidroponiese stelsel is gebruik vir die sifting van die teikeneienskappe, insluitende waterverliese van uitgesnyde blare, blare se relatiewe waterinhoud, spesifieke blaaroppervlakte, aantal waterlote en aantal blare, en lengteverwante parameters soos wortellengte (RL) en lootlengte (SL). Varsgewigparameters het ingesluit wortels se vars gewig (RFW), lote se vars gewig (SFW), blare se vars gewig (LFW) en die totale plant se vars gewig (TPFW). Droëgewigparameters het ingesluit wortels se droë gewig, lote se droë gewig, blare se droë gewig (LDW), bogrondse droë gewig en die totale plant se droë gewig (TPDW). Bykomende eienskappe het ingesluit chlorofilinhoud-indeks (CCI), stomakonduktansie, fotosintetiese aktiewe straling, blaaroppervlakte-indeks, stralingsgebruikdoeltreffendheid, relatiewe groeitempo (RGR) en wortel-tot-lootverhouding. Roessiekteweerstand-genotipes is uit die bestudeerde populasie geïdentifiseer. Molekulêre karakterisering van die roesweerstandgene wat uit die koringgenotipes verkry is, het ŉ toename in die alleelfrekwensies in MS-MARS-siklusse een tot twee vir sowel vroulike as manlike lyne getoon, meer spesifiek Lr34 en Sr2. Die manlike lyne het egter laer alleelfrekwensies en afwesigheid van die Lr19-merker in die populasie getoon. Die variansieontleding (ANOVA) het getoon dat waterstres die groei en -ontwikkeling van koringgenotipes vir al die bestudeerde eienskappe aanmerklik beïnvloed, behalwe die RL en NT. Die gekose vyf genotipes het die beste waterstresweerstand getoon van al die eienskappe wat bestudeer is. Die genotipes is op grond van hul prestasie onder waterstresomstandighede in die volgende rangorde geplaas: 15HYLD-30, 15HYLD-22, 15HYLD-29, 15HYLD-18 en 15HYLD-26. Sterk positiewe assosiasie (SPA) wat onder waterstresomstandighede by vasgewigkomponente waargeneem is, het LFW en RFW (r = 0.884) ingesluit, gevolg deur TPFW met varsgewigkomponente soos RFW (r = 0.848), SFW (0.922) en LFW (r = 0.920). SPA is ook opgeteken vir SFW en SL (r = 0.832), CCI met SL (r = 0.835) en SFW (0.890) en, laastens, TPDW met RGR (r = 0.879) en LDW (r = 0.872). SPA opgeteken onder waterryke omstandighede, naamlik TPFW, het SPA met SFW (0.872), LFW (r = 0.920) en TPDW met SL (r = 0.877) en LDW (r = 0.841) getoon.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/104987
Masters Degrees (Genetics) 
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