Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/4/2007
Publication Date: 12/1/2007
Citation: Anderson, J.A., Chao, S., Liu, S. 2008. Molecular Breeding Using a Major QTL for Fusarium Head Blight Resistance in Wheat. Crop Science. 47(3):S112-S119 Interpretive Summary: Fusarium head blight, a disease caused by a fungal pathogen and commonly known as scab, has devastated the wheat growing regions in the US, especially the Northern Great Plains. Extensive breeding efforts are being directed at improving host plant resistance throughout the region in an attempt to develop resistant cultivars. The inheritance of disease resistance is complex, and susceptibility to disease is strongly influenced by environmental conditions. In other words, disease damage might be low during dry growing seasons and potentially severe during wet seasons. The genes controlling the inheritance of such a trait are termed quantitative trait loci, or QTLs. To develop cultivars with better resistance, breeders often seek high levels of disease resistance from non-adapted germplasm resources as donors, and bring them into elite cultivars through crossing. Breeding lines resistant to disease are typically selected by means of conventional disease screening in the field, which is imperfect and time consuming. To complement the disease screening process, a small amount of leaf tissue can be collected from the breeding lines and subjected to DNA marker screening using the tagged DNA markers that are found closely-associated with the QTLs. This process is called marker-assisted selection (MAS). However, several barriers to using MAS for a QTL must be addressed before MAS can be integrated into a breeding program, including: 1) its efficiency/gain compared to conventional selection; 2) the usefulness of markers in breeding-relevant plant populations; and 3) the cost, throughput, and expertise required. The main resistance source being used by breeders in this region is Sumai 3, a resistant cultivar developed in China. A major QTL with a significant effect on disease resistance, and originating from Sumai 3, has been located on the short arm of wheat chromosome 3B (3BS) and has been tagged using DNA markers. This QTL has been validated and has consistently improved the level of resistance after being transferred into different genetic backgrounds or recipient cultivars. Therefore, the large effect of this QTL and the consistent expression of the trait justify complementing the extensive disease screening efforts with MAS for this major QTL. Further study of the 3BS chromosome region containing the major QTL resulted in the development of a diagnostic DNA marker that can correctly predict which plant materials contain this gene. The establishment of the USDA-ARS Regional Small Grains Genotyping Centers has dramatically increased the ability to apply MAS to cereal breeding by providing access to high throughput DNA extraction and genotyping equipment. However, the number of individual plants that can be subjected to MAS is limited due to the capacity of the genotyping centers. To efficiently use the resources provided by the centers, a process of retrospective breeding was adopted to identify those populations that are most likely to produce cultivar candidates. In the future, more efficient DNA extraction technologies and marker platforms will allow us to fully implement MAS in breeding programs.
Technical Abstract: The difficulties of breeding for Fusarium head blight resistance, a quantitatively inherited fungal disease, caused us to initiate a marker-assisted (MAS) approach to accelerate our gains from selection. Although MAS for simply inherited traits has become commonplace in many plant breeding programs, there are few examples of its application with quantitatively inherited traits. Several barriers to MAS for a QTL must be addressed before it can be integrated into a breeding program, including: 1) its efficiency/gain compared to phenotypic selection; 2) the usefulness of markers in breeding-relevant populations; and 3) the cost, throughput, and expertise required. We identified a major QTL, Fhb1, for Fusarium head blight resistance in wheat and validated its effect in an additional mapping population and near-isogenic lines developed from segregating lines in our breeding program. The effect of this QTL was large and consistent enough to justify complementing our extensive phenotypic screening efforts for this disease with MAS for this major QTL. Fhb1 is located in a highly polymorphic region and we developed highly diagnostic markers while fine mapping this QTL. The establishment of the USDA-ARS Regional Small Grains Genotyping Centers has dramatically increased our capabilities to apply MAS by providing access to high throughput DNA extraction and genotyping equipment. Because a limited number of individuals can be subjected to MAS, we use a process of retrospective breeding to identify those populations that are most likely to produce cultivar candidates. More efficient DNA extraction technologies and marker platforms will allow us to fully implement MAS in breeding programs.