Toward positional cloning of Fhb1, a major QTL for Fusarium head blight resistance in wheat

DNA markers near Fhb1, a major QTL for Fusarium head blight resistance on chromosome 3BS in wheat, were used to screen the Chinese Spring chromosome 3B BAC library, and a BAC contig spanning the Fhb1 region was constructed. The genic regions of two overlapping BAC clones were sequenced. Based on new DNA markers developed from the BAC sequences, Fhb1 was narrowed down to a 261 kb region with seven putative genes. The expression of the candidate genes was examined by RT-PCR. Four out of the seven genes are expressed in wheat spikes. But, there is no clear expression difference between water-inoculated and Fusarium-inoculated wheat spikes. Five cosmid clones containing all seven candidate genes were isolated from a cosmid library of Sumai 3. The cosmid clones were used to transform FHB-susceptible cultivar Bobwhite and transgenic plants were obtained for all cosmid clones. Transgenic plants for four out the five cosmid clones have been tested for Type II resistance to FHB, and none of them are resistant. FHB evaluation of the transgenic plants of the fifth cosmid clone is in progress. A highly diagnostic, codominant marker, UMN10 was developed and used for MAS for gene Fhb1.