Transfer of polygenic resistance to ryegrass mosaic virus from perennial to Italian ryegrass by backcrossing

Polygenic resistance to ryegrass mosaic virus (RMV) was transferred from perennial to Italian ryegrass cv. Tribune by repeated cycles of backcrossing, polycrossing and selection. The resulting synthetic variety (Bb 2113) was highly resistant to infection by RMV whereas the Italian ryegrass cultivars Tribune, RvP, Bartolini, Augusta, Wilo and Dalita all were highly susceptible. Leaf width and length of Bb 2113 was similar to that of cv. Tribune and, like Tribune, Bb 2113 had awned florets. In a field trial, Bb 2113 had a similar persistency rating and number of inflorescences in the regrowth to cv. Tribune but produced 11% less dry matter. The results emphasise the need for a more efficient means of transferring small numbers of genes from one species of Lolium to another than backcrossing provides.