Doctoral Degrees (Food Science)

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Browsing Doctoral Degrees (Food Science) by browse.metadata.advisor "Fox, Glen"

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    Genotyping South African wheat germplasm for hardness alleles
    (Stellenbosch : Stellenbosch University, 2019-04) De Groot, Gerida; Manley, Marena; Fox, Glen; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Wheat grain kernel hardness (GKH) is one of the most important quality properties of wheat (Triticum aestivum). The molecular basis of GKH is determined by the combination of Puroindoline a (Pina- D1) and b (Pinb-D1) alleles in a wheat cultivar. The current study investigated the Pin alleles present in commercial South African (SA) wheat cultivars. Wheat production regions in South Africa are diverse; and divided into the summer rainfall irrigation (SRI) and winter rainfall dryland (WRD) regions where spring wheat is planted, as well as the summer rainfall dryland (SRD) region where facultative and winter wheat are planted. Nine commercial wheat cultivars, differing in GKH, were planted at four locations per region, with three replications, over three production seasons (2012 – 2014). After each season, the wheat grain was harvested followed by determination of kernel characteristic, milling yield, flour and dough quality properties. The Pin allele identities, of the 27 cultivars, were determined using polymerase chain reaction and allele sequencing. Four Pin allelic genotypes were identified. Wheat cultivars produced in the WRD region showed no diversity in Pin genotypes. GKH prediction models, based on the Pin allele identities of the samples, were thus developed for only the SRI and SRD production regions. Following analysis of variance (ANOVA) and Pearson’s correlations of the WRD region, where the cultivars had identical Pin genotypes, it was shown that genotype (G) primarily contributed to variation in GKH in the Swartland region. GKH correlated negatively with break flour yield (BFY), total flour yield (TFY) and α-amylase activity. Environment (E) primarily contributed to variation in GKH in the Rûens region, where GKH had negative correlations with BFY and TFY. In addition, negative GKH correlations were observed with kernel weight and diameter, and positive correlations with flour ash content, water absorption, dough strength, -stability, and -tenacity. Wheat cultivars of the SRI and SRD regions were subjected to ANOVA, with cultivars nested within Pin genotypes. Wheat containing the Pina-D1b/Pinb-D1a genotype had increased GKH, flour water absorption (FWA), dough tenacity and alveograph P/L ratio; however, decreased kernel weight, diameter, BFY, TFY, dough extensibility, -strength, -stability, and tolerance to overmixing, compared to the Pina-D1a/Pinb-D1b genotype. The Pinb-D1p mutation had decreased kernel weight, diameter, dough extensibility, and swelling index; with increased BFY and TFY, FWA, dough development time, -strength and -tenacity compared to the Pinb-D1b and Pinb-D1ab mutations. The molecular weight distribution of proteins within wheat cultivars of different Pin genotypes were determined with size exclusion high performance liquid chromatography. ANOVA with nested design and Pearson’s correlations showed environmental influence, and G x E interaction, primarily contributed to the variation in all protein fractions. The Pina-D1b/Pinb-D1a and Pina-D1a/Pinb-D1b genotypes showed decreased sodium dodecyl sulphate (SDS) -soluble monomeric protein with increased kernel hardness. In contrast the Pina-D1a/Pinb-D1b genotype showed decreased SDSsoluble polymeric protein and increased SDS-insoluble monomeric protein. This study contributed valuable knowledge on the Pin alleles present in SA wheat cultivars as well as the influence of Pin genotype combinations and Pinb-D1 allele mutations on the GKH and processing quality. The influence of Pin genotype and GKH on the molecular weight distribution of proteins were also demonstrated. This will enable SA wheat breeders to select specific Pin allele combinations to more rapidly breed wheat for specific end-use purposes.