Evaluation of Zinfandel Heritage Selections
No evaluation of the Heritage selections can be made while comparing selections of unknown virus status. Relying on visual inspections every effort was made to take selections that were free of virus. We knew, however, that tests would have to be made to confirm the virus status of the selections. Initial steps were taken toward understanding virus status of the selections very early in the history of the Heritage Vineyard.
In 1991 Dr. Deborah Golino and FPMS took 3 selections for woody indexing of virus. In 1997 six more selection went to FPMS for woody indexing. In 1999 all the selections in phase I and II were surveyed for virus using polymerase chain reaction (PCR) at FPMS.
Selections 4, 5 and 6 were indexed beginning in 1991. They were found by woody indexing to be free of virus exclusive of grapevine rupestris stem pitting associated virus (RSP), which two had. This was not surprising since we know that vines grafted on St. George rootstock are almost always infected with RSP. The two selections testing positive for RSP are now in the process of having the virus removed by shoot tip culture. Tests should be complete this year and results will be reported in next year?s report.
Selections 10, 25, 46, 53, 60 and 61 were delivered to FPMS in 1997 for woody indexing. In addition to RSP that 5 selections had, 4 had grapevine leafroll associated virus (GLR) and one tested positive for grapevine fanleaf virus (GFLV). The selection with GFLV was immediately removed from the vineyard. All of these selections, including the GFLV positive selection, are now in the process of having the virus removed by shoot tip culture.
The PCR testing completed in 1999 yielded mixed results, a complete table of results can be found in our report submitted in 2001. After discussion with Dr. Golino we have decided not to consider fleck as a damaging virus and have removed it from consideration. Polymerase chain reaction detection of virus in grapevines is now felt to be more sensitive than traditional woody indexing. For this reason beginning last year all new material coming into FPMS undergoes both PCR and woody indexing. It is important to this project to note that the three selections that underwent woody indexing for virus were all found to be free of GLR. The PCR test however, found all three to be infected with GLR 4,5 complex. From this point forward, we will use PCR as the definitive virus test for this project. Of the viruses tested for GLR was by far the most common with 46%of the selections infected with one or more of the GLR complexes. Interestingly, only one selection that was free of GLR was found to have one of the other viruses. The number of selections testing positive for GLR was not anticipated, teaching us once again that the lack of red leaves in fall is far from being assuring a negative virus status.
Dr. Golino has performed these tests free of charge for the project and we are indebted to her and FPMS for their cooperation and support. Only selections that are free of virus (not including Fleck or RSP) will be considered for a replicated trial of these selections and further data collected will be presented indicating virus status. In 1998 we began viticultural evaluations of the selections in Phase 1. These measurements are taken at harvest and include °Brix, pH, TA, berry weight, yield per vine, cluster weight, cluster number and pruning weight per vine. Collection of yield per vine and clusters per vine did not begin until 1999.