Grafting vegetable plants can improve plant health and yields (Rivard and Louws, 2008). Although grafting improves the resistance of plants to various soilborne diseases, vegetable grafting has its challenges. Cutting devices used to sever stems can provide an ideal mode of transmission of disease inoculum of viral origin. Although all plants can be subject to infection by mechanical transmission of viruses (Boyle et al., 1997), crops such as heirloom tomatoes are especially prone to infection because they do not have virus resistance. Another important factor contributing to disease is the increased use of grafting in combination with high tunnels, greenhouses, or open-field production, creating the ideal situation for transmission of viral disease as a result of tool contamination and mechanical and human activity (Cohen et al., 1999; Lewandowski et al., 2010).
Although transmission of TSWV, a tospovirus, by plant extracts has been reported (Betti, 1992; Zitter, 2006), the most recognized source of transmission is thrips (Kumar et al., 1993). On the other hand, the tobamoviruses including ToMV can be transmitted mechanically through contact with soil, water, or foliage (Antignus et al., 1990; Hollings, 1976; Hollings et al., 1975). Both of these diseases are economically important in the United States and worldwide. In addition, reports of viral diseases as a result of the use of virus-contaminated rootstocks have been reported in melons (Choi, 2001). Tobamoviruses are easily moved by human intervention and once introduced can easily result in further plant-to-plant dissemination (Choi, 2001). In some cases, this can lead to epidemic levels when virus-contaminated rootstocks are used (Chen et al., 2006). Tomato is especially vulnerable to virus movement as a result of the number of manual operations that must be performed such as grafting and pruning, which are effective methods of virus dissemination. Therefore, the objectives of the research were to determine: 1) the efficiency of a single cut of a virus-infected tomato plant stem to move the virus during grafting; 2) the effect of an infected scion or the rootstock on virus transmission in a grafting system; and 3) if visual diagnosis can be used as a method of eliminating virus-infected plants.
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