THE POSSIBLE EPIDEMIOLOGICAL SIGNIFICANCE OF POLLEN AND SEED TRANSMISSION IN THE CHERRY LEAF ROLL VIRUS/BETULA SPP. COMPLEX

A virus serologically related to isolates of cherry leaf roll virus (CLRV) from Prunus avium (L.) L. and Sambucus nigra L. was transmitted to a range of herbaceous plants from leaves, roots or pollen of 53 of 64 trees of Betula spp. growing at heathland sites in Berkshire, Leicestershire and Oxfordshire. In the season after inoculating foliage of clonal P. avium F12/1 with a virus isolated from birch, 10 were systemically infected with noticeable leaf rolling, delayed bud break and leaf bronzing.

Three isolates of CLRV from B. verrucosa Ehrh. growing in widely separated parts of the United Kingdom possessed few, if any, antigenic determinants not held in common. Significantly, the virus was transmitted in pollen to four of 114 birch seedlings and was present in two of 73 progeny produced by a naturally infected mother tree which received virus-free pollen. Up to 22% of seed collected from open pollinated and naturally infected birch trees carried virus.