Technical Yearbook 2023

FIGURE 2. ELISA for the detection of viruses. 1) A virus specific antibody is stuck to the sides and bottom of a small plastic well, and all unbound antibodies are washed away. 2) Sap from a vine is added to the well. 3) If virus is present (red route), the virus will stick to the antibody. All unbound plant material is then washed away. 4) Where the virus is stuck (red route), the addition of a second antibody to the virus will cause it to stick to the free parts of the virus. This antibody is chemically coupled with an enzyme and is called a conjugate. Unbound conjugate is washed away. Where no virus is found in the well (black route) the conjugate will not stick and is totally washed away. 5) By adding the substrate of the enzyme, a colour reaction takes place in the well where the conjugate is stuck to the virus (red route) (A), but where there is no virus no colour reaction takes place (B). The colour, which can be measured, therefore shows the presence of the virus.

traits indefinitely under constant environmental conditions. This is especially important for grape growers who want to reproduce the highest-quality plants and berries that have consistent properties for use as table grapes or in winemaking. A further advantage of vegetative propagation is that plants bypass the immature seedling phase and therefore reach the mature phase sooner. This can save a lot of time and money in commercial plant production. The main disadvantage of large-scale vegetative propagation is the danger of narrowing the biodiversity of a species. Also, if a particular plant clone is susceptible to certain diseases, there is potential to lose entire crops, as all the plants would have the same level of susceptibility. Furthermore, the virus disease status of a mother plant is passed onto most, if not all the plantlets derived through vegetative propagation, as viruses would often be systemically distributed throughout the original plant. The international trade in grape propagation has been a very common means of international spread of viruses historically, and of the more than 80 viruses infecting grapevines, most are globally distributed. Furthermore, the process of grafting grapevine scions onto rootstocks,

along with vegetative propagation of grapevines, have in the past resulted in grapevine plants having multiple virus infections. Over the past three decades, grapevine vegetative propagation has however generally been accompanied by virus elimination and virus management processes to ensure healthy planting material. The most common means of grapevine virus elimination is the use of heat therapy and meristem tip culture (figure 1). Control of viruses in a vegetatively propagated crop such as grapevines can conveniently be divided into processes that prevent international virus spread (quarantine and phytosanitary regulation), and those that prevent local spread (certification). In the former, plant material distributed from one country to another is either placed in quarantine on entry and tested for viruses which are not known to occur in the importing country, or accompanied by a certificate from the exporting country that declares the plant material tested and free of specific exotic viruses, or stating that the exporting country does not contain those viruses. Local control of virus spread in vegetatively propagated crops, including grapes, is primarily through certification schemes that ensure the production of planting

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TECHNICAL YEARBOOK 2023