Submitted to: California Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2002
Publication Date: 5/1/2002
Technical Abstract: In 1986, young 'Black Beaut' plum trees in two orchards in Dinuba, CA showed bark necrosis and gummosis on scaffold branches and the main trunk, and the woody cylinders were severely pitted. The disease was given the name plum bark necrosis-stem pitting PBNSP). This situation occurred because scions of 'Wickson' plum, that appeared to be healthy, but were in fact infected, had been whip grafted on every second-leafed 'Black Beaut' tree. All the grafts failed, but the disease agent was transmitted into the trees. We were interested in determining the host responses to this particular disease agent and providing descriptions of the symptoms hoping to prevent further occurrences of the disease and provide diagnostic information to growers and advisors. We evaluated the responses of several Prunus species and varieties to infections by the PBNSP agent. 2 or 3 trees per variety were graft-inoculated in September 1997, with multiple bark tissues or peach bud chips. Trees that were not grafted served as healthy controls. The source of the PBNSP inoculum was diseased 'Black Beaut' plum trees on 'Nemaguard' peach rootstock. With the single exception of 'French Improved' plum trees, virus infections in all of the other graft-inoculated test plants, with and without leaf or bark-stem symptoms, were positive. Healthy plants were found negative in a laboratory assay (such as RT-PCR) developed specifically for the associated disease agent. Based on sequence information obtained, we designed new primers, and the primer combination yielding a specific product (541 bp [base pair]-size DNA) that was used in all RT-PCR assays of test plants. In order to minimize serious virus-disease outbreaks in commercial orchards, growers should always request certified propagation materials identified in the R&C Program. This will help to ensure that virus-tested sources are collected and used in their orchards.