Prune Brownline Disease: Susceptibility of Prune Rootstocks and Tomato Ringspot Virus Detection

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Abstract
Tomato ringspot virus (TmRSV) was readily graft-transmitted to prune (P. domestica) trees on peach (P. persica) and Myrobalan plum (P. cerasifera) rootstocks and a brownline symptom developed at the scion rootstock union when TmRSV-infected root chip inoculum from prune brownline (PBL)-affected orchard trees was grafted to rootstocks of trees. However, TmRSV was not transmitted and PBL did not develop in trees on Marianna 2624 plum (P. cerasifera .times. P. munsoniana) clonal rootstock similarly graft-inoculated with root chip inoculum from the same source. In addition, TmRSV isolates associated with the PBL, peach yellow bud mosaic, Prunus stem pitting, cherry leaf mottle and California peach stem pitting diseases all infected and induced brownline formation at the scion/rootstock union of graft-inoculated prune trees on peach and Myrobalan, but not those on Marianna 2624, rootstocks. TmRSV was consistently detected by direct and indirect enzyme-linked immunosorbent assay (D-ELISA and I-ELISA, respectively) and by radioimmunosorbent assay (RISA) in peach and Myrobalan plum rootstocks of trees naturally affected by PBL; however, I-ELISA and RISA were more reliable than D-ELISA for detecting TmRSV in diseased trees. Xiphinema californicum transmitted TmRSV-PBL to cucumber (Cucumis sativus) and to seedlings of the standard prune rootstocks, peach and Myrobalan plum. Apparently, Marianna 2624 plum is resistant or immune to TmRSV infection, so control measures for PBL should include the use of trees propagated on Marianna 2624 plum instead of Myrobalan plum or peach rootstocks at sites threatened or affected by diseases caused by TmRSV.