Guwela, Veronica Faith
(2023)
High zinc wheat for sub-Saharan Africa.
PhD thesis, University of Nottingham.
Abstract
Zinc deficiency affects over 17% of the global population. Risk deficiencies of up to 96% have been reported in Sub Saharan Africa, mostly due to increased poverty levels and high dependence on cereal diets with low bioavailable zinc. In Africa, although wheat provides up to 20% of dietary energy, cultivated wheat is inherently low in essential micronutrients such as grain zinc (Zn) and iron (Fe), and the genetic variability is relatively narrow. Genetic biofortification of food crops is considered a sustainable and cost-effective approach for alleviating mineral nutrient deficiencies. Wheat progenitors and wild relatives are considered as potential sources of genetic variation for crop improvement. Inductively coupled plasma mass spectrometry (ICP-MS) was undertaken to determine the natural variation in grain Zn and selected essential mineral nutrients (Fe, Ca and Se) of wheat wild relative accessions, in order to identify novel sources of genetic variation. Accessions from the genus Triticum, Aegilops, Thinoprum, Amblyopyrum and Secale were screened. Results showed a wide variation in grain Zn, Fe, Ca and not Se. Triticum urartu and Amblyopyrum muticum accessions showed the highest grain Zn and Fe, whilst Thinopyrum species showed the highest Ca concentration. A preliminary study of 48 pre-breeding introgression lines (doubled haploids) derived from T. urartu and Am. muticum also showed a wide variation in grain Zn, Fe, Ca and not much in Se.
Selected T. urartu and Am. muticum doubled haploid (DH) lines were also phenotyped under two contrasting soil types, to investigate the effects of soil type on grain Zn, Fe, Se and Ca concentration. One soil type was characterised by higher Zn, Fe, and lower pH (Chitedze soils), and the other soil type was characterised by lower Zn, Fe and higher pH (Ngabu soils). Analysis of variance (ANOVA) revealed a ~two-fold higher grain Zn concentration in low pH, higher Zn soils compared to high pH, lower Zn soils. Variation in grain Zn concentration was associated with the genotypes, soil type, and the interaction between soil and genotypes. Grain Fe concentration was influenced by genotypes and soil type only, grain Se was highly influenced by soil type whilst grain Ca was independent of soil type but highly influenced by genotypes and partly by the interaction between genotype and soil type.
Two high-Zn DH lines (DH-348 and DH-254) were selected, and crossed with three Malawian wheat varieties (Kadzibonga, Kenya nyati and Nduna), to transfer the Am. muticum and T. urartu chromosome segments potentially increasing grain mineral concentration in the DH lines. From the crossing program, 41 Malawian wheat/Am. muticum and 11 Malawian wheat/ T. urartu BC1F3 introgression lines were generated. A field based phenotyping study of the 11 Malawian wheat/T. urartu and the 37 Malawian wheat/ Am. muticum alongside three Malawian wheat, DH-348, DH-254, Paragon, Pavon 76 and Chinese Spring showed high yields and 11-30 mg kg-1 improvement in grain Zn in 11 introgression lines, above the three Malawian wheat varieties and Chinese Spring and Paragon. These lines also showed 8-12 mg kg -1 improvement in grain Fe than Nduna and Kenya nyati, whilst four lines showed a 6-10 µg kg -1 Se concentration improvement above paragon and the three Malawian checks. Across the four experiments, grain Zn showed strong and significant positive correlations with grain Fe concentration. Grain Ca moderately and significantly correlated with grain Zn and Fe, whilst grain and straw Zn, Fe, Ca and Se showed positive and low significance or positive but insignificant associations. Grain Zn and Fe also showed significant negative correlations with TKW/yield.
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