Barley chromosome location and expression of dwarf bunt resistance in wheat addition lines

Barley (Hordeum vulgare) is resistant to dwarf bunt of winter wheat (Triticum aestivum) caused by Tilletia controversa. Nine wheat-barley addition lines were utilized to determine which barley chromosomes and chromosome arms carry resistance genes. The lines included six disomic addition lines, WB1, WB2, WB3, WB4 WB6, and WB7, and three ditelosomic addition lines, WB5S (containing the short arm of barley chromosome 5), WB6S (containing the short arm of barley chromosome 6), and WBL6 (containing the long arm of barley chromosome 6). These lines, their parent cultivars, and susceptible winter wheat cv. Wanser were inoculated with spores of T. controversa at the two-leaf stage. The barley parent, Betzes, showed no infection and only 5 of 401 heads of addition line WB6 were infected. Lines WB1, WB2, WB3, WB4, and WB7, and cvs. Wanser and Chinese Spring showed a high incidence of infection. WB6S had significantly lower bunt incidence (0 to 1%) than WB6L or WB5S. Lines WB6L and WB5S had a high incidence of infection. This suggests that the short arm of barley chromosome 6 carries the dwarf bunt resistance gene(s). The incidence of bunt infection in wheat-barley hybrid plants was examined. Hybrids were regenerated from embryo rescue followed by F-1 inflorescence culture of wheat-barley crosses and by embryo rescue followed by induction of somatic embryos directly from culture of the immature embryos. Both methods resulted in production of amphiploid plants as well as haploid hybrids (n = 28). Infection incidence in crosses with zero, one, and two copies of the barley genome in a wheat background was 64, 30, and 1%, respectively, suggesting a dosage effect associated with the resistance gene(s). The female wheat parent influenced the expression of barley resistance gene(s) in these wheat-barley hybrids.