Modern tomato breeding has led to improvements in postharvest attributes including shelf life, but this has come with a noticeable decrease in fruit flavor (Klee, 2010). Educated consumers have begun demanding heirloom tomatoes for their superior flavor and unique appeal (Bland, 2005; Jordan, 2007; Klee, 2010). This increased interest has helped expand a niche market for local organic growers (Jordan, 2007). However, heirloom tomatoes can be difficult to grow in Florida as a result of high pest and disease pressure. One of the major pest management challenges is RKNs (Meloidogyne spp.), which thrive in warm weather and moist, sandy soils (Roberts et al., 2005; Sasser, 1980). RKNs cause root galls that damage the root system and result in stunted plant growth and significant yield loss. RKNs persist in the soil for many years and have a broad host range. These characteristics make RKN difficult to control on organic farms. The small size of many organic farms may prevent use of the long rotation times needed to ameliorate soil conditions between planting of susceptible crops.
Organic growers often face pest and disease challenges with few effective control methods, making organic heirloom tomato production even more difficult and potentially less profitable than conventional production (Rivard and Louws, 2008; Rivard et al., 2010a). With the use of appropriate rootstocks, grafting may be a useful technique for vegetable producers to overcome soilborne pathogens including RKN. Vegetable grafting began in Japan and Korea in the 1920s to manage fusarium wilt (caused by Fusarium oxysporum Smith) in watermelons and is currently widely used in cucurbitaceous and solanaceous crop production in Asian and Mediterranean countries (Lee, 1994; Lee et al., 2010).
Recently, growers and researchers in the United States have begun examining vegetable grafting as an integrated pest management tool for successful vegetable production. Research has focused on grafted seedling production, use, and economics (Kubota et al., 2008; Rivard et al., 2010b); grafting as an alternative to methyl bromide in field production (Freeman et al., 2009); and the use of resistant rootstocks for controlling RKN and soilborne diseases such as bacterial wilt [caused by Ralstonia solanacearum (Smith) Yabuuchi et al.], fusarium wilt, and southern blight (caused by Sclerotium rolfsii Sacc.) (Bausher, 2009; López-Pérez et al., 2006; Rivard and Louws, 2008; Rivard et al., 2010a). With the phase-out of methyl bromide for soil fumigation and the continued rise in demand for organic produce in the United States, the need for alternative disease control methods that do not rely on synthetic biocides has increased (Greene et al., 2009; King et al., 2008; Louws et al., 2010).
Tomato hybrids (Solanum lycopersicum L.) and interspecific tomato hybrids (S. lycopersicum × S. habrochaites S. Knapp & D.M. Spooner) have been used worldwide as disease-resistant rootstocks in grafted tomato production (King et al., 2010). It is unclear how the differences between tomato hybrid rootstocks and interspecific tomato hybrid rootstocks will affect field production of indeterminate heirloom tomatoes. Hence, rootstock evaluations for heirloom tomato production in open-field conditions should involve both types of rootstocks. Field studies conducted in North Carolina demonstrated that southern RKN [M. incognita (Kofoid & White) Chitwood] could be managed by grafting heirloom tomatoes onto interspecific hybrid rootstocks (Rivard et al., 2010a). However, the inconsistent function of the Mi resistance gene in these rootstocks suggested the need for more examinations of rootstock performance in fields infested with RKN to provide recommendations for effective use of rootstocks. Interest in tomato grafting is emerging among small and organic growers in Florida. The results from the North Carolina studies are promising and suggest that grafting may be applicable in Florida heirloom tomato production. However, appropriate rootstocks for Florida conditions need to be determined.
The purpose of this study was to assess heirloom tomato grafting for RKN control under organic production in naturally infested Florida sandy soils. It is hypothesized that grafting onto resistant rootstocks can reduce nematode galling incidence. Tomato hybrid and interspecific tomato hybrid rootstocks were compared with respect to their influence on nematode resistance, crop vigor, and fruit yield.
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