Fusarium diseases of cereals are a persistent threat to food and feed safety. Growing resistant cultivars is the most effective strategy in reducing losses from Fusarium head blight (FHB) infection. Although numerous FHB resistance QTL have been identified only few have been validated and fine-mapped. Qfhs.ifa-5A (Buerstmayr et al. 2003) is among the best validated resistance QTL. It predominantly contributes resistance to fungal entry with the favorable allele descending from the highly Fusarium resistant wheat cultivar Sumai-3. Qfhs.ifa-5A resides in the low-recombinogenic pericentromeric region of chromosome 5A making fine-mapping extremely difficult. Genotyping 3650 near isogenic recombinant inbred lines for recombination between the QTL flanking markers partitioned the Qfhs.ifa-5A interval into 12 bins1. All NILs that recombined at the QTL interval were phenotyped for FHB, anther retention and plant height. A strong positive correlation was observed between anther retention and FHB severity and plant height showed a moderate negative correlation with FHB severity. Composite interval mapping separated the Qfhs.ifa-5A interval into two QTL. The major effect QTL Qfhs.ifa-5Ac mapped across the centromere and the smaller effect QTL Qfhs.ifa-5AS mapped to the distal half of 5AS. Although Qfhs.ifa-5Ac and Qfhs.ifa-5AS were delimited to genetic intervals as small as 0.1 and 0.2 cM, the corresponding physical distances were large and comprised 44.1 Mbp and 49.2 Mbp, respectively. Sumai-3 alleles at either QTL significantly improved resistance and reduced anther retention suggesting a pleiotropic effect of anthers on Fusarium resistance. This hypothesis was further supported by an experiment using Remus and its near isogenic line NIL3 carrying the Qfhs.ifa-5A alleles. Through removing anthers resistant NIL3 and susceptible Remus became almost equally resistant and were significantly less diseased than their control variants without anther manipulation at early time points after inoculation. At late time points the positive effect of anther removal became smaller for Remus and disappeared completely for NIL3. Results clearly showed that absence of anthers primarily enhanced resistance to initial infection while it did not protect plants from fungal spreading within the spikes.

The knowledge of increasing anther extrusion as a major resistance component of Qfhs.ifa-5A will assist in gene identification by suggesting candidates for further analysis/reverse genetics.