Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/15/2017
Publication Date: 8/31/2017
Citation: Rosskopf, E.N., Pisani, C., Di Gioia, F. 2017. Crop-specific grafting methods, rootstocks and scheduling-tomato. Book Chapter. https://www.ars.usda.gov/research/publications/publication/?seqNo115=346557.
Interpretive Summary: The use of grafting to manage soilborne pest problems in vegetable production systems has been used for many years in other parts of the world. It is only recently, with the loss of methyl bromide for soil fumigation, that interest in grafting has grown in the United States. Interest in grafting has led to the identification of crop-specific practices that optimize both grafting success and use of grafted plants in the field. Grafting of tomatoes in particular has been useful for the production of ‘heirloom’ specialty tomatoes because these plants have no resistance to soilborne diseases. The use of grafted tomatoes provides a tool for the management of soilborne diseases such as bacterial and Fusarium wilts for which there are few options.
Technical Abstract: Grafting has gained popularity as a method to manage plant diseases previously controlled by soil fumigation with methyl bromide. Some of the most significant soilborne pest problems for which resistant rootstocks may be beneficial include root-knot nematodes (Meloidogyne spp.; Kokalis-Burelle and Rosskopf, 2011; Barrett et al., 2012a), Verticillium wilt (Verticillium albo-atrum and V. dahliae), and southern blight (Athelia rolfsii anamorph Sclerotium rolfsii). Bacterial wilt, caused by Ralstonia solanacearum is a significant concern for tomato producers in many regions. It has been reported that inadequate control of bacterial wilt with soil fumigants such as methyl bromide, chloropicrin, and a combination of chloropicrin and 1,3-dichloropropene. The pathogen has a wide host range and persists in the soil for long periods of time, making crop rotation ineffective, forcing farmers to abandon fields as losses can reach 100% rapidly. Additionally, tomato varieties with resistance to bacterial wilt often produce small, unmarketable fruit. Thus, some tomato cultivars available that carry genetic resistance are used as rootstocks and cultivars that provide desirable fruit characteristics as scions, making grafting to manage bacterial wilt in tomatoes an important option for the tomato industry. For some diseases, rootstocks may have to be selected with resistance to a specific race of the pathogen. This is the case for rootstocks resistant to Fusarium oxysporum f.sp. lycopersici (Fol) the cause of Fusarium wilt in tomato. Many of the rootstocks that are commercially available have resistance to races 1 and 2 of this pathogen, as well as resistance to the crown rot pathogen, F. o. f.sp. radici-lycoperisici, as is the case for the interspecific hybrid ‘Maxifort’ (S. lycopersicum × S. habrochaites), one of the commonly used tomato rootstocks. Fewer commercial rootstocks are available that also have resistance to race 3 of Fol, which is more limited in its distribution but is becoming increasingly more common, particularly in the southeastern United States. Cleft, side, and splice grafting are the three main grafting techniques used to graft tomatoes. However, splice grafting, also known as “Japanese top-grafting” or “tube-grafting”, is the most commonly used technique when grafting Solanaceous crops. Sanitation is extremely important for successful grafting as plant pathogenic bacteria and viruses can be passed from plant-to-plant from hands, cutting surfaces, and tools. Therefore, particular care is required in cleaning the grafting area and cleaning or changing razor blades frequently. When grafting, regardless of the method used, it is critically important to have good contact between the scion and rootstock vascular systems. This is accomplished by grafting plants with similar stem diameters. Plants should be grafted when plants have 2-4 true leaves and stem diameters between 2-2.5 mm. To this purpose, is important to define the grafting timeline. A germination test is recommended prior to a grafting event in order to determine how long both the scion and the rootstock will take to reach the optimal size and time seeding accordingly. It is recommended to keep plants in a shaded area prior to grafting and to cease watering 12-24 hours prior to grafting. This will prevent water from pushing the scion away from the rootstock. The tube or splice grafting is achieved by cutting the rootstock and scion stems at a 30-45° angle, and putting the cut edges of the two plants in close contact with the help of grafting clips. It is important to cut the rootstock below the cotyledons to avoid unwanted rootstock regrowth, requiring additional pruning. The scion can be cut below or above the cotyledon, wherever the stem diameter best matches the rootstock. Grafted tomatoes can be produced for use in the open field or under “protecte