Marker-assisted backcross breeding for Fusarium head blight resistance in South African wheat

English: In our modern era with the global population soon to reach the nine billion mark, there are rising concerns about food security. There is a driven need for more sustainable food production. Wheat is considered one of the most important cereal crops grown worldwide. However, wheat production in SA has been declining steadily over the last decade. A shift in SA wheat production has occurred from winter dryland to irrigated spring wheat being planted in a maize-wheat crop rotation system. Wheat production is vulnerable globally and locally due to yield losses and grain damage caused by sporadic FHB disease outbreaks, which are predominantly caused by F. graminearum. Currently the number of FHB resistant wheat cultivars available in SA is limited and not adequate. The aim of this study was to develop FHB resistant lines through backcross breeding and MAS to track the introgression of targeted FHB resistance genes/QTL (Fhb1, Fhb2, Qfhs.ifa-5A QTL and 7A QTL) into the SA wheat cultivar Krokodil. The use of a MABC pre-breeding programme to transfer targeted FHB resistance genes/QTL from FHB resistant donor CM-82036 into the background of SA spring wheat cultivar Krokodil is discussed. F1 individuals from which a BC1F1 generation was developed were validated using SSR marker Gwm493, which is linked to the Fhb1 gene. Marker-assisted foreground selection was done for targeted FHB resistance genes/QTL combined with background selection against unwanted donor alleles. A partial linkage map of targeted chromosomes 3B, 5A, 6B and 7A was generated from a BC1F1 population consisting of 120 individuals. Based on this linkage map GGT profiles were developed for each individual which allowed analysis and comparison of recombination events on these chromosomes. Families containing three and four targeted FHB resistance genes/QTL were identified. These lines were backcrossed to Krokodil to yield a BC2F1 population of 238 individuals. Simultaneously, a phenotypic validation glasshouse trial was done on additional individuals of the BC1F1 population to confirm expression of the targeted FHB resistance genes/QTL. Spray and point inoculation methods were used to evaluate Type I and Type II FHB resistance responses on six selected controls and 130 segregating BC1F1 genotypes. These BC1F1 individuals were genotyped using markers associated with targeted FHB resistance genes/QTL. FHB disease symptoms were expressed as a percentage infection per spike and assessed 4, 7, 10, 14, 18 and 21 dpi. BC1F1 genotypes containing the targeted Fhb1 gene in combination with the Qfhs.ifa-5A QTL contributed additively to overall FHB resistance and the prevention of expected yield loss. Preliminary results indicated that the Fhb1 gene reduced the presence of tombstone kernels. The Fhb1 gene in combination with the Qfhs.ifa-5A QTL were successfully transferred using MAS and validated phenotypically in the background of Krokodil displaying improved FHB resistance levels. Since the primary objective was improvement of FHB resistance, this study successfully identified 44 BC2F1 individuals that contained the FHB resistance gene Fhb1 and/or the Qfhs.ifa-5A QTL. A partial linkage map across all 21 wheat chromosomes was generated by testing 120 polymorphic SSR markers on these 44 individuals. With the aid of GGT profiles the RPGP analysis was done for each BC2F1 individual. Sixteen high value lines that contained Fhb1 and/or the Qfhs.ifa-5A QTL with a minimum RPGP value of 80% were identified and selected for further analysis. Eight elite lines that contained the targeted FHB resistance genes/QTL as well as the potential for good baking quality were selected for further development. Lines identified and recommended from this study can be used to initiate the further development of FHB resistant wheat cultivars in SA.