Valued at $1.24 billion, fresh market tomato is the second most valuable vegetable crop grown in the United States [U.S. Department of Agriculture (USDA), 2016]. The southeastern United States accounts for ≈52% of the total planted acreage in the United States, which has a total value of $699 million. Ralstonia solanacearum race 1 is an economically devastating soilborne pathogen that affects tomato throughout the southeastern United States (Ji et al., 2007; McAvoy et al., 2012). Soil fumigation with traditional fumigants, such as chloropicrin and the now banned methyl bromide, have proven ineffective in the management of this pathogen (Chellemi et al., 1997; Driver and Louws, 2002; Enfinger et al., 1979).
Grafting of susceptible tomato cultivars onto resistant rootstocks is an effective cultural technique for managing BW (McAvoy et al., 2012; Rivard and Louws, 2008). This practice is widely used throughout many Asian and Mediterranean countries where intensive greenhouse production is prevalent (Besri, 2001; Cohen et al., 2007; Lee, 2003; Lee et al., 1998). Interest in grafting continues to increase in the United States, and demand for grafted plants has led to the establishment of grafting-specific facilities.
Currently, at least 65 tomato rootstocks have been developed by commercial breeders (USDA, 2014). Many of these rootstocks contain the same resistance packages; for example, 20 of the 65 rootstocks are purported to be resistant to BW. Limited comparative research exists evaluating many of these rootstocks, thus growers face challenges when deciding which rootstock to use. Furthermore, levels of BW resistance among certain rootstocks do not appear to be equal (McAvoy et al., 2012). McAvoy et al. (2012) noted that certain rootstocks may improve yield compared with nongrafted plants when grown in conditions with low amounts of BW. Research using grafted tomato grown in greenhouses and open-field conditions lacking any history of soilborne pathogens has shown that certain rootstocks can increase fruit size, weight, and count compared with nongrafted controls (Kyriacou et al., 2017). Whether the improved yield from grafted plants in locations with low amounts of BW observed by McAvoy et al. (2012) was due to differing BW-resistance mechanisms or a more general rootstock-mediated yield increase is unknown.
To address the lack in information on commercially available BW-resistant rootstocks, we conducted the following study with the objectives of 1) assessing BW resistance of three resistant rootstocks in a commercial tomato field with known history of BW infestation, 2) determine whether there are yield benefits or penalties when using these rootstocks in conditions with no recent history of BW in open field production, and 3) compare the effects of grafting on yield in different climatic regions of North Carolina.
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