Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/1998
Publication Date: N/A
Interpretive Summary: Scab is a destructive disease of wheat. It is caused mainly by a fungus named Fusarium graminearum. In addition to wheat, this fungus can infect barley, oats, and rye, and cause 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 grains 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 special environmental conditions needed to initiate test infections. Our objective was to molecularly tag the genes most important for scab resistance in selected Chinese wheat varieties so they could be rapidly moved into U.S. wheat varieties. In this study, we succeeded in identifying a chromosomal region from a Chinese wheat variety that contains one or more genes that are primarily responsible for limiting the spread of the scab fungus from kernel to kernel within wheat heads. The results of these studies will speed the production of new scab resistant wheat varieties by allowing researchers to quickly determine whether this chromosomal region that confers scab resistance is present within their new wheat varieties. If it is possible to limit the spread of the fungus, losses to wheat producers and the levels of mycotoxin within the harvested grain should be reduced.
Technical Abstract: Scab is a destructive disease of wheat. To accelerate development of scab-resistant wheat cultivars, molecular markers linked to scab resistance genes have been identified by using recombinant inbred lines (RILs) derived by single-seed descent from a cross between the resistant wheat cultivar Ning 7840 and the susceptible cultivar Clark. In the greenhouse, F5, F6, F7 and F10 families were evaluated for resistance to spread of scab within a spike by injecting about 1000 conidiospores of Fusarium graminearum into a central spikelet. Inoculated plants were kept in moist chambers for 3 days to promote initial infection and then transferred to green house banches. Scab symptoms were evaluated four times from 3 to 21 days after inoculation. The frequency distribution of scab severity indicated that resistance to spread of scab within a spike was controlled by a few major genes. DNA was isolated from both parents and 133 F9 families. A total of 300 combinations of AFLP primers were screened for polymorphism using bulked segregant analysis. Twenty pairs of primers revealed at least one polymorphic band between the two contrasting bulks. The segregation of each of these bands was evaluated in 133 RILs. Eleven AFLP markers showed significant association with scab resistance and each of them could explain up to 53% of the total variation (R2). The markers with high R2 values mapped to a single linkage group. By interval analysis, one major QTL for scab resistance explaining up to 60% of the total variation for scab resistance was identified and tentatively mapped to chromosome 7B. Some of the AFLP markers may be useful in marker-assisted breeding to improve resistance to scab in wheat.