Analysis of Double-Stranded RNAs from Cherry Trees with Stem Pitting in California

Five distinct dsRNA species were recovered from Bing sweet cherry (Prunus avium (L.) L.) trees with stem pitting symptoms. A 4.7-kilobase pair (kbp) dsRNA was isolated from mahaleb rootstock (P. mahaleb L.); an unrelated 4.7-kbp dsRNA, always co-purified with a 1.3-kbp dsRNA, and a 9-kbp dsRNA were from Bing cherry. In addition, an 8.5-kbp dsRNA found in diseased Shirofugen flowering cherry and in Bing cherry was identified as sour cherry green ring mottle virus (CGRMV). The larger, 8.5- and 9.0-kbp dsRNA species were graft-transmissible, while the smaller ones were non-transmissible and appeared cryptic in nature. Reverse transcription-polymerase chain reaction (RT-PCR) assays were developed for each dsRNA species by cloning and sequencing cDNA synthesized from the dsRNA templates. When several diseased collections were assayed by RT-PCR, approximately 14% reacted positively with primers for the 9.0-kbp dsRNA or CGRMV. Although CGRMV and the 9.0-kbp dsRNA caused wood-marking symptoms in graft-inoculated Mazzard (P. avium) seedling trees, no xylem or canopy symptoms developed in grafted Bing cherry. The causal agent or agents of cherry stem pitting have not been identified.