Peach red marbling and peach sooty ringspot, two new virus-like degenerative diseases of Prunus

More than 600 Prunus samples were examined by using a nonradioactive digoxi genin-labelled RNA probe specific for hop stunt viroid (HSVd). Prunus salic ina and Prunus armeniaca appeared to be better hosts than Prunus persica. T he weak viroid concentration in flowers and young leaves of peach trees gro wing in the field did not permit its detection in such samples. The diagnos is was more reliable (about 85%) with bark and leaves aged 4 months and mor e, from regrowths of GF 305 peach seedlings inoculated and kept in the gree nhouse. Detection of HSVd in leaves and bark of apricot and Japanese plum p lants aged 3 months or more also proved reliable (about 80% and 90%, respec tively). HSVd could be transmitted in apricot, peach and plum nucleic acid preparations to GF 305 peach seedlings by repeated stem slashing, and to ch erries (Prunus avium and Prunus serrulata) by approach grafting with an inf ected P. salicina source. The viroid was eliminated from 18% of the clones obtained after thermotherapy. In the course of this study, 25 selected Prunus accessions suspected to be infected by unusual diseases were analysed by hybridization with a HSVd-spe cific probe and by indexing on GF 305 peach seedlings in the greenhouse. Fi fteen of these accessions were found to be infected by HSVd, 19 induced red dish marbling, and four induced small blackish spots on the leaves aged abo ut 4 months. Repeated assays showed that these foliar symptoms were not cau sed by the viroid. Peach red marbling (PRMa) has not been associated with a ny known virus and seems to be caused by an infectious agent not yet descri bed. That could also be the case with the agent of peach sooty ringspot (PS RS). PRMa and PSRS symptoms were reproduced by grafting and indexing, and t heir causal agents eliminated by thermotherapy in a significant fraction of the treated plants. They behave like viral agents and can infect the diffe rent Prunus species studied.