Tomato yellow leaf curl virus, a begomovirus, was first described in Israel in 1939 (Picó et al., 1996), and subsequently became a major constraint to tomato production in the entire Mediterranean basin (Czosnek et al., 1990). TYLCV is transmitted by the SPW and considered the most damaging virus of tomato worldwide (Picó et al., 1996). After acquiring the virus, the SPW remains viruliferous for life, with symptoms appearing ≈2 to 3 weeks after inoculation (Lapidot and Polston, 2006). In the western hemisphere, TYLCV was first detected in Cuba in 1990, the Dominican Republic in 1992, and Florida in 1997 (Polston et al., 1999). TYLCV is now endemic throughout most of the southern tier of the United States, including Florida, Georgia, North Carolina, Louisiana, Texas, and California (Isakeit et al., 2007; Moriones and Navas-Castillo, 2010; Polston and Schuster, 2000; Rojas et al., 2007). Symptoms of TYLCV infection include dwarfed leaves that are up-curled, thick and crumpled, and have chlorotic margins. Up to 90% of flowers may abscise after infection, resulting in poor fruit set and yield, especially when infections occur early in the season (Schuster et al., 1996).
Tomato growers in Florida have largely focused on controlling the SPW vector to reduce yield losses from TYLCV (Polston, 2003; Schuster et al., 1996). Management of SPW and TYLCV can be achieved through applications of insecticides, particularly systemic neonicotinoids. However, SPW resistance has developed to this class of insecticides in Florida (Schuster et al., 2008, 2010) and elsewhere (Horowitz et al., 2007). An effective cultural control program would include reduction of vector populations by initiating timely crop destruction after harvest followed by maintenance of a host-free period over one or more SPW generations (Hilje et al., 2001; Polston, 2003). The effective use of a host-free period to manage TYLCV in the Dominican Republic was studied by monitoring TYLCV levels in SPW using polymerase chain reaction with TYLCV-specific primers (Salati et al., 2002). The incidence of TYLCV decreased markedly during the host-free period, and then gradually increased during the tomato-growing season. In contrast, TYLCV persisted in SPW and tomato plants in an area in which the host-free period was not implemented. Unfortunately, the length of the growing season in southern and central Florida has been increasing due to higher market prices and increased production of grape tomato and alternate hosts of TYLCV such as pepper. As a result, the tomato-free planting period is generally not long enough to eliminate the problem of TYLCV (Polston, 2003). These deficiencies in the present management system are posing a serious threat to the 32,000 acres of round and Roma-type tomato in Florida valued at $564 million [U.S. Department of Agriculture (USDA), 2013]. Therefore, viable alternative management tools are needed.
Tomato varieties resistant to TYLCV could obviate or reduce the necessity of pesticide applications and/or plant seclusion (greenhouses or shadehouses) and could provide a stable and sustainable management alternative (Polston, 2003). Progress in breeding for TYLCV resistance was initially slow, due in part to the complex genetics of resistance and the presence of interspecific barriers between the wild and domesticated tomato species (Brunetti et al., 1997). Furthermore, until recently, most of the improved genetically resistant material has come from Israel. It is important for southern Florida to have a breeding and variety testing program under local environmental conditions and directed at existing market requirements. TYLCV-R varieties and germplasm adapted to the hot and humid Florida environment are now being developed by BHN Seed (Immokalee, FL), Harris Moran Seed Co. (Modesto, CA), Seminis Vegetable Seeds (Oxnard, CA), Syngenta Co. (Golden Valley, MN), University of Florida Tomato Breeding Program (Balm, FL), Sakata Seeds (Morgan Hill, CA), Hazera Seeds (Coconut Creek, FL), and others.
Evaluations of TYLCV-R varieties and germplasm have been conducted in Florida (Cushman and Stansly, 2006; Gilreath et al., 2000; Scott, 2004); however, this study provides information needed to revise current recommendations including new varieties and breeding lines previously not evaluated under low and high TYLCV pressure. Relative to susceptible varieties, such as Florida 47, Sebring (round), and Mariana (Roma-type), TYLCV-R varieties evaluated produced comparable yields under low virus pressure and greater yields under high virus pressure. However, resistant varieties have yet to be widely grown in Florida, probably due to a perception of lower fruit quality compared with traditional varieties such as Florida 47 and Sebring. Additionally, TYLCV-R varieties should also have resistance to other common diseases such as Fusarium crown rot (Fusarium oxysporum f.sp. radicis-lycopersici) and bacterial leaf spot [BLS (Xanthomonas vesicatoria, Xanthomonas euvesicatoria, Xanthomonas perforans, and Xanthomonas gardneri)]. The goal of this study was to compare the yield and quality of round and Roma-type tomato varieties/advanced breeding lines with resistance/tolerance to TYLCV to the current industry standards.
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