VIRAL TWIG NECROSIS OF SWEET CHERRY - MODES OF TRANSMISSION AND SPREAD OF PETUNIA ASTEROID MOSAIC-VIRUS (PEAMV)

Grafting symptomless scions, derived from petunia asteroid mosaic viru s (PeAMV)-infected trees, to healthy rootstocks resulted in only 3.3% infection in the resulting trees. Up to 90% of seeds from infected swe et cherries contained high quantities of PeAMV, but the virus was not transmitted to the seedlings apparently because of low virus content i n the embryo and loss of infectivity during seed maturation and storag e. Replanting healthy cherry trees cv. Sam, grafted to different roots tocks, into contaminated soils resulted in new infections. Eight of 13 trees on rootstocks derived from Prunus avium (F 12/1 and cv. Sam on its own roots) were infected with PeAMV within a period of four years but only one of 16 trees on Weiroot-rootstocks (selections from Prunus cerasus) became infected. The detection of PeAMV in naturally contami nated soil samples by the bait plant procedure, using Nicotiana clevel andii, was superior to testing soil eluates by enzyme-linked immunosor bent assay (ELISA) and immune electron microscopy (IEM). Wild plants m ay contribute to virus propagation and maintenance of virus contaminat ion of the soil as 25 of 310 samples from 712 herbaceous plants growin g in the vicinity of infected trees contained PeAMV; the contaminated samples represented 12 species. The perpetuation of PeAMV by infected scion wood is probably of minor significance, and infection via the so il probably represents the most important means of spread of viral twi g necrosis in northern Bavaria.