The interaction between Prunus necrotic ringspot virus and Prune dwarf virus in peach stunt disease

A field trial comparing the effects on peach of infection by either Primus necrotic ringspot virus (PNRSV) or Prune dwarf virus (PDV) alone, and infection with both viruses (peach stunt disease-PSD) was established. The integrity of the viral treatments was assessed using ELISA. Data for yield and tree growth characteristics were collected. No spread of either virus was detected until the 5(th) year after planting, by which time 3 years of data had been accumulated and the trial was discontinued. Trees infected with PSD showed premature defoliation at the end of the first growing season after inoculation. Infection by either virus alone did not cause premature defoliation. Trees infected with both viruses displayed bark splitting and increased watersprout (sucker) production. Fruit yields were reduced by up to 60% in trees infected with both PNRSV and PDV. Experiments on small trees involving similar viral treatments were completed in the greenhouse. Measurements of shoot growth were made and the number of leaves produced per shoot counted. The Julian date for bud-break for each tree was recorded. At two-week, intervals after bud break, total RNA was extracted from leaves at corresponding positions on each tree. RNA samples were analysed in Northern blots using anti-sense cRNA probes labelled with biotin and detected using the chemiluminescent substrate CDP-Star (TM). Reductions in both shoot growth and the number of leaves produced were observed and a delay in bloom date was also noted. Effects of viral infection were clearly influenced by the rootstock used (Lovell or Nemaguard) and the scion variety being examined (GF305, Elberta, or Garnet Beauty). Northern blots showed that the presence of PNRSV reduced by up to 17-fold the amount of RNA 3 of PDV present in trees of GF305 and Elberta infected with both viruses. This interaction at the molecular level is unlike previously characterized synergistic viral diseases and presents a unique opportunity for study of the interaction between viruses and the host plant at the molecular level.