|dc.description.abstract||Wheat (Triticum spp.) is one of the most important cereal crops produced worldwide. South Africa is the largest wheat producer in sub-Saharan Africa (SSA). However, wheat production in South Africa is affected by many biotic, abiotic and socio-economic constraints. Among the biotic stresses, Fusarium head blight (FHB) is one of the most important fungal diseases of wheat caused predominantly by Fusarium graminearum. Various strategies have been proposed to control FHB epidemics. Genetic control, which includes host plant resistance, is currently the most economically and environmentally friendly approach for controlling FHB. Breeding for FHB resistant wheat cultivars provides the potential for long-term, sustainable control of FHB. Consequently, a pre-breeding of wheat has been undertaken at the Agricultural Research Council-Small Grain Institute (ARC-SGI) in collaboration with global and regional wheat researchers to develop FHB resistant genetic pool. A larger number of genetic resources was acquired from collaborators and about 778 new recombinant inbred lines (RILs) were developed through designed crosses and continuous selfing and selection. As part of this initiative, this study was undertaken with the following objectives: 1) to determine the field response of the 778 newly developed RILs and standard check varieties of wheat for FHB resistance and to identify sources of resistance for breeding or direct production, and 2) to determine FHB resistance among 76 wheat lines using field based phenotyping and to determine the genetic background of 11 selected most resistant lines and four susceptible checks using simple sequence repeat (SSR) markers in order to identify novel FHB resistance sources.
A total of 778 RILs were field evaluated for their FHB reaction across four environments, along with resistant and susceptible checks, Sumai 3 and SST 806, respectively. The analysis of variance showed significant differences among the genotypes, the testing environments and their interactions. FHB resistance was found to be heritable with heritability estimate of 64%. Among the 778 RILs evaluated, 6% had an infection rate <20%, suggesting high FHB resistance among the lines. Overall, five RILs were selected as new sources of high FHB resistance. These lines were 681 (Buff/1036/71), 134 (Duzi/910/8), 22 (Bav/910/22), 717 (Bav/937/8) and 133 (Duzi/910/7) with FHB scores comparable to the resistant check. These lines can be recommended for further breeding or direct production.
Seventy three wheat genotypes were obtained from CIMMYT. These lines were phenotypically characterized for FHB reaction and 14% of the most resistant lines with economic agronomic traits were selected for further characterization using 24 SSR markers linked to known FHB resistance genes. Haplotype profiles of the selected FHB resistant wheat lines were compared to known sources of FHB resistance in order to identify and characterize possible genes conferring resistance in the lines. Three CIMMYT entries were found to have allelic similarities with the FHB resistant lines. These entries included #937, #936 and #930 with FHB resistance genes such as Fhb1, Fhb5 and Fhb2, respectively. The rest of the selected CIMMYT lines showed no similarities to the known resistance sources, implying that they hold novel FHB resistance genes. This will allow for the enrichment of the FHB resistant genepool and diversification of FHB resistance sources. The selected wheat lines are valuable genetic resources for FHB resistance breeding programs.||en_US