Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2001
Publication Date: N/A
Interpretive Summary: Scab is a destructive disease of wheat that is caused by a fungus named Fusarium graminearum. In addition to wheat, this fungus infects barley, oats, and rye, and causes stalk rot in corn. Wheat scab significantly reduces wheat grain yield and quality, resulting in billions of dollars in crop losses annually. The fungus also produces mycotoxins that limit the consumption of infected grain by humans and livestock. While it is sometimes possible to use fungicides to control the disease, the costs are often prohibitive. If scab resistant wheat varieties were developed, they could represent cost efficient and effective means of limiting losses caused by the disease. However, producing scab resistant wheat varieties by traditional breeding methods has been difficult because of the genetic complexity of scab resistance and the variability of environmental conditions that influence the development of the disease. The objectives of this study were to molecularly tag genes for scab resistance in a Chinese wheat variety so they can be rapidly moved into U.S. wheats. In a previous study, we produced markers linked to a gene that provides most of the scab resistance from the Chinese wheat. In this study, we identified the chromosomal locations of those markers and therefore the gene. In addition, we identified markers for and the chromosomal location of another gene that, while not as important as the first, significantly contributed to scab resistance. The results of these studies will be of interest to researchers who are working to produce new scab resistant wheat varieties, which should reduce economic losses to wheat producers and reduce the levels of mycotoxin within harvested grain.
Technical Abstract: Breeding for scab resistance currently relies mainly on laborious phenotypic evaluations, influenced by environmental factors. Molecular marker associated with scab resistance genes would facilitate selection. A major QTL for Type II resistance was previously identified using ECORl-AFLP markers in recombinant inbred lines (RILs) derived from Ning 7840 (resistant) x Clark (susceptible). We used PstI-AFLPs and single nucleotide polymorphism markers (SNPs) in thaumatin-like protein (TLP) genes to improve the coverage of the EcoRl-AFLP map. The PstI-AFLP markers located the major QTL on chromosome 3BS, and identified a new QTL on chromosome 6BS. The best marker at this new QTL explained 17.5% of the phenotypic variation of scab resistance. Degenerate oligonucleotide primers based on conserved sequences of TLP genes were used to amplify genomic sequences from wheat. Amplification products were obtained that shared high homology with known TLP genes. Mapping of point mutations within sequences of the TLP genes identified two SNPs on chromosomes carrying QTLs for type II resistance. The possibility of using the resistance genes themselves as molecular markers, and/or candidate genes for map based cloning is discussed in relation to Type II scab resistance.