Grapevine collections free from pathogens: tools and their application

The grapevine collections are very important tools to maintain grapevine biodiversity and historical germoplasm as well however in several cases especially grapevine from poor cultivated or non commercial varieties could be infected by several graft transmissible pathogens such as viruses, phytoplasmas and other systemic bacteria. In the majority of the cases these pathogens are not inducing evident symptomatology in short time after grafting therefore the possibly infected material of collection could represent a dangerous pathogen reservoir. In order to control pathogen presence in already made collections and to prevent the spreading of the above pathogens together with the grapevine germplasm to other collections. Then, it is mandatory to exclude presence of quarantine pathogens such as “flavescece dorée” (FD) phytoplasmas and advisable to exclude relevant pathogens for quality such as viruses and phytoplasmas agent of “bois noir”, by using the most sensitive detection techniques available. It is advisable however to acquire any possible information concerning the phytosanitary status of the circulating grapevine material in order to prevent possible unforeseen outbreak of disease such as those occurred for FD disease when a grapevine insect such as Scaphoideus titanus (previously named Scaphoideus littoralis) was introduced in Europe. It is known in fact that a high number of different phytoplasmas are able to infect grapevine worldwide in the presence of appropriate insect vector or by grafting or micropropagation techniques application and crown gall is an old severely remerging disease at least in the major viticultural areas of EU and US. First step before transferring germplasm among collection must be the verification of their sanitary status taking into account that tests to verify virus and bacteria presence should be carried out preferably during winter/spring time while those to detect phytoplasmas are more sensitive in Summer and Fall periods and the most sensitive techniques such as ELISA and PCR must be employed. In the case of germplasm having no clean plants available after the survey it is necessary to clean the material using thermotherapy and or shoot tip culture in order to eliminate the pathogens. These techniques are not eliminating the pathogens from all the produced material therefore molecular tests are again necessary to assess the grapevine health status before the material can be employed for collection and/or field dissemination. In case of virus or phytoplasma infected grapevine germplasm of unique genetic value it must be maintained under insect proof condition while it is infected in order to avoid contamination of other germplasm in the same collection. In the same way the clean germplams should also be protected in insect proof environment in order to avoid its recontamination. It is also very important to keep the collection clean from insect that are virus (mealy bugs and scale insects) or phytoplasma vectors (leafhopper and cixiids) and also the soil must be clean from Agrobacterium tumefaciens and collection should be protected from frost or mechanical damages increasing crown gall dissemination.