Introgression of crown rust (Puccinia coronata) resistance from meadow fescue (Festuca pratensis) into Italian ryegrass (Lolium multiflorum) and physical mapping of the locus

Resistance was found in the meadow fescue (Festuca pratensis) to crown rust (Puccinia coronata), originating from ryegrasses (Lolium spp). A backcrossing programme successfully transferred this resistance into diploid Italian ryegrass (Lolium multiflorum) and genomic in situ hybridisation (GISH) was used to identify the introgressed fescue chromosome segment. The resistant (R) plants in two BC3 lines all carried an introgressed segment on a single chromosome, which in one of the lines was confined to the short arm of the chromosome. Susceptible (S) plants either contained no introgressed chromosome segment or a segment which was physically smaller than the segments in resistant plants. Using GISH the resistance locus could be physically mapped to the midpoint of a short arm. Segregation ratios of the progeny of BC3 plants, when crossed as R S and R R, were in agreement with the hypothesis that the resistance was controlled by a single gene or very closely linked genes. No R plants were produced by crossing S S plants.