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

[摘要] English: In our modern era with the global population soon to reach the nine billion mark, thereare rising concerns about food security. There is a driven need for more sustainable foodproduction. Wheat is considered one of the most important cereal crops grownworldwide. However, wheat production in SA has been declining steadily over the lastdecade. A shift in SA wheat production has occurred from winter dryland to irrigatedspring wheat being planted in a maize-wheat crop rotation system. Wheat production isvulnerable globally and locally due to yield losses and grain damage caused by sporadicFHB disease outbreaks, which are predominantly caused by F. graminearum. Currentlythe 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 breedingand 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 MABCpre-breeding programme to transfer targeted FHB resistance genes/QTL from FHBresistant donor CM-82036 into the background of SA spring wheat cultivar Krokodil isdiscussed. F1 individuals from which a BC1F1 generation was developed were validatedusing SSR marker Gwm493, which is linked to the Fhb1 gene. Marker-assistedforeground selection was done for targeted FHB resistance genes/QTL combined withbackground selection against unwanted donor alleles. A partial linkage map of targetedchromosomes 3B, 5A, 6B and 7A was generated from a BC1F1 population consisting of120 individuals. Based on this linkage map GGT profiles were developed for eachindividual which allowed analysis and comparison of recombination events on thesechromosomes. Families containing three and four targeted FHB resistance genes/QTLwere identified. These lines were backcrossed to Krokodil to yield a BC2F1 population of238 individuals. Simultaneously, a phenotypic validation glasshouse trial was done onadditional individuals of the BC1F1 population to confirm expression of the targeted FHBresistance genes/QTL. Spray and point inoculation methods were used to evaluate TypeI and Type II FHB resistance responses on six selected controls and 130 segregatingBC1F1 genotypes. These BC1F1 individuals were genotyped using markers associatedwith targeted FHB resistance genes/QTL. FHB disease symptoms were expressed as apercentage infection per spike and assessed 4, 7, 10, 14, 18 and 21 dpi. BC1F1genotypes containing the targeted Fhb1 gene in combination with the Qfhs.ifa-5A QTLcontributed additively to overall FHB resistance and the prevention of expected yieldloss. Preliminary results indicated that the Fhb1 gene reduced the presence of tombstone kernels. The Fhb1 gene in combination with the Qfhs.ifa-5A QTL weresuccessfully transferred using MAS and validated phenotypically in the background ofKrokodil displaying improved FHB resistance levels. Since the primary objective wasimprovement of FHB resistance, this study successfully identified 44 BC2F1 individualsthat contained the FHB resistance gene Fhb1 and/or the Qfhs.ifa-5A QTL. A partiallinkage map across all 21 wheat chromosomes was generated by testing 120polymorphic SSR markers on these 44 individuals. With the aid of GGT profiles theRPGP analysis was done for each BC2F1 individual. Sixteen high value lines thatcontained Fhb1 and/or the Qfhs.ifa-5A QTL with a minimum RPGP value of 80% wereidentified and selected for further analysis. Eight elite lines that contained the targetedFHB resistance genes/QTL as well as the potential for good baking quality were selectedfor further development. Lines identified and recommended from this study can be usedto initiate the further development of FHB resistant wheat cultivars in SA.

[发布机构] University of the Free State