A spontaneous segmental deletion from chromosome arm 3DL enhances Fusarium head blight resistance in wheat

Much effort has been directed at identifying sources of resistance to Fusarium head blight (FHB) in wheat. We sought to identify molecular markers for what we hypothesized was a new major FHB resistance locus originating from the wheat cultivar "Freedom" and introgressed into the susceptible wheat cultivar "USU-Apogee". An F_2:3 mapping population from a cross between Apogee and A30, its BC₄ near-isoline exhibiting improved FHB resistance, was evaluated for resistance. The distribution of FHB resistance in the population approximated a 1:3 moderately resistant: moderately susceptible + susceptible ratio. Separate disease evaluations established that A30 accumulated less deoxynivalenol and yielded a greater proportion of sound grain than Apogee. Molecular mapping revealed that the FHB resistance of A30 is associated with molecular markers on chromosome arm 3DL that exhibit a null phenotype in A30 but are present in both Apogee and Freedom, indicating a spontaneous deletion occurred during the development of A30. Aneuploid analysis revealed that the size of the deleted segment is approximately 19% of the arm"s length. Our results suggest that the deleted interval of chromosome arm 3DL in Apogee may harbor FHB susceptibility genes that promote disease spread in infected spikes, and that their elimination increases FHB resistance in a novel manner.