Foundation Plant Services (FPS) at the University of California, Davis performs virus testing and elimination and maintains the rose Foundation Collection of over 800 virus-tested rose accessions (including eight rootstocks). New introductions, called “candidate selections,” are typically sent to FPS as dormant, bareroot plants. Candidate selections may originate as AARS winners, advanced selections of a rose hybridizer, or the proprietary selection of a commercial rose nursery. There is also a growing interest in bringing historic or “heritage” roses into the program to ensure that they are available free of rose mosaic. After potting and labeling, plants are placed outdoors at the FPS nursery to grow under ambient conditions.
Propagating rose cuttings.
Disease testing for viral pathogens is the first step for inclusion of a candidate selection into the collection. Laboratory tests are conducted for apple mosaic virus (ApMV), blackberry chlorotic ringspot virus (BCRV), Prunus necrotic ringspot virus (PNRSV), rose spring dwarf-associated virus (RSDaV), rose yellow vein virus (RYVV) and rose rosette virus (RRV). When initial testing demonstrates that a rose cultivar is infected with a viral pathogen, heat therapy or tissue culture procedures are begun for virus elimination. All tissue culture selections and plants that were propagated from heat-treated buds must undergo final laboratory testing to determine whether the virus elimination treatment was successful. (Learn more by reading Virus Elimination using Tissue Culture in Roses – this will be in the Roses E&O material – provide link on italicized title). Once diagnostic tests are negative, rooted cuttings of the candidate selection are propagated in FPS greenhouses in preparation for establishment in the field collection.
Only when the candidate selection is found negative for targeted viruses are the plants finally planted in the FPS rose Foundation collection. Whenever possible, new introductions are planted as own rooted plants to reduce the possibility of introducing virus through an infected understock and to prevent the problems associated with rootstock suckering. The FPS rose collection is regularly retested for reoccurrence of virus. The plants are also visually inspected in the spring for virus symptoms. As the selections mature, the rose collection is carefully examined for correct identification and trueness to type. FPS holds regular meetings with professional rose propagators and breeders who inspect the collection. Any selection that is not up to standard is rogued out. If questions arise about the identity or productivity of a selection, it is flagged in the computer database, restricting distribution until a conclusive determination is made by industry representatives. The quality of the rose program is enhanced as the rose production industry reports back on its experience with the plant materials originating from the FPS rose program.
Bundling dormant rose cuttings before distribution.