The resistance of two clones of perennial ryegrass and their progeny to ryegrass mosaic virus from different parts of Britain

SUMMARY Two clones (R1 and R2) of perennial ryegrass selected from cv.S.23 pastures for immunity to a few isolates of ryegrass mosaic virus (RMV) retained immunity when inoculated manually with isolates from 10 widely-separated sites in Britain and when grown outside at eight other sites for 1 yr. At a ninth site (Saxmundham) an isolate (RMV-Sax) capable of infecting both resistant clones (although only with difficulty) was detected in one plot. Resistance to a Rothamsted isolate of RMV and to RMV/Sax was also shown by R1 × R2 progeny. Clone R1 yielded more than S.23 in small field plots as did R1 × R2 and R2 × R1 progeny in a pot experiment.