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Leslie D. Hintz, Renee R. Boyer, Monica A. Ponder, Robert C. Williams and Steven L. Rideout

Tomatoes have been associated with numerous outbreaks of salmonellosis in recent years. Trace-backs suggest tomato fruits may become contaminated during preharvest. The objective of this study was to determine the potential for Salmonella enterica serotype Newport to be internalized into the roots, stems, leaves, and fruit of red round tomato plants through contaminated irrigation water at various stages of plant development. Tomato plants were irrigated with 250 or 350 mL (depending on growth stage) of 7 log CFU·mL−1 S. Newport-contaminated irrigation water every 7 days. Roots, stems, leaves, and two tomato fruit from plants irrigated with S. Newport or water (negative control) were sampled for contamination at five stages of growth. Twenty-five of the 92 total samples taken from plants irrigated with S. Newport were confirmed positive (serovar specificity was not evaluated). Sixty-five percent of confirmed samples were roots, 40% were stems, 10% were leaves, and 6% were fruit. There was a significant difference in the presence of S. enterica according to tissue sampled (roots > stems > leaves, and fruit) (P < 0.05) and no association between growth stage and contamination (P > 0.05). Contamination of tomato fruit with S. Newport introduced through irrigation water is low because a high level of persistent contamination of a plant in the agricultural setting is unlikely.

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Hyun-Gyun Yuk, Benjamin R. Warren and Keith R. Schneider

Infiltration and survival of a rifampicin-resistant five-serovar Salmonella cocktail was investigated in laser-etched tomatoes (Lycopersicum esculentum) and smooth (untreated) and punctured (dye solution only) tomato surfaces in storage for 14 days at 25 °C/60% relative humidity. Surviving Salmonella populations were enumerated on tryptic soy agar supplemented with the antibiotic rifampicin. In the first survival study (laboratory-etched tomatoes), the population of Salmonella spp. in wounds increased to 6.8 log cfu/fruit, whereas cells on smooth surfaces decreased to undetectable levels during 14 days of storage. For etched tomatoes, the storage reduced 2.7 log cfu/fruit after the first 3 days; however, an increase was observed at 7 days, followed by a population decreased to 2.9 log cfu/fruit at 14 days. In the second survival study (pilot plant-etched tomatoes), the populations decreased a total of 3.5 log cfu/fruit and 2.5 log cfu/fruit comparing 1 day with 14 days for smooth and etched surfaces respectively. Infiltration of the dye solution or Salmonella beyond the area of immediate tissue damage was not observed on any tomato surface tested.

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Bielinski M. Santos, John W. Scott and Maricruz Ramírez-Sánchez

‘Tasti-Lee’™ (‘Fla. 8153’) is the first tomato (Solanum lycopersicum) released in Florida exclusively for the premium specialty market, with characteristic superior flavor and elevated lycopene concentration. Research was conducted to determine the appropriate nitrogen (N) fertilization and in-row distances for ‘Tasti-Lee’ tomato and thus improving the opportunities for successful adoption for this cultivar. Three N fertilization programs and two in-row distances were tested. Total N rates (204, 239, and 274 lb/acre) were the result of the combination of 50 lb/acre of N during prebedding plus each of the following drip-applied N fertilization programs: 1) 1.5 and 2.0 lb/acre per day from 1 to 4 weeks after transplanting (WAT) and 5 to 12 WAT, respectively; 2) 1.5, 2.0, and 2.5 lb/acre per day during 1 to 2 WAT, 3 to 4 WAT, and 5 to 12 WAT; and 3) 1.5, 2.5, and 3.0 lb/acre per day during 1 to 2 WAT, 3 to 4 WAT, and 5 to 12 WAT, respectively. In-row distances were 18 or 24 inches between plants, providing 5808 and 4356 plants/acre. Early and total marketable yields of ‘Tasti-Lee’ tomato were influenced by in-row distances and N fertilization programs, but not by their interaction. The highest early marketable fruit yield was found in plots treated with the highest N rate among fertilization programs (+6%), and in plots planted 18 inches apart (+7%) in comparison with the lowest N rate and the 24-inch spacing. Tomato plots treated with the highest N rate (274 lb/acre) resulted in the largest total marketable yield (+8%). Among the in-row distances, when plants were transplanted 18 inches apart, tomato total marketable yield increased by 18% compared with 24 inches between plants.

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James P. Gilreath and Bielinski M. Santos

Two independent field studies were conducted to determine the efficacy of methyl iodide (MI) formulations and rates on mixed nutsedge [purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus)] stands and their effects on tomato (Solanum lycopersicum) yields. In both studies, treatments were rates of two formulations of MI + chloropicrin (Pic) at the 98:2 (v/v) and 50:50 (v/v) proportions. In the MI + Pic 98:2 study, the fumigant rates were 0, 100, 125, 150, 175, and 200 lb/acre in Spring 2004 and 0, 125, 150, 175, and 200 lb/acre in Fall 2004. In the MI + Pic 50:50 study, the rates were 0, 200, 250, 300, 350, and 400 lb/acre during both seasons. Additionally, a grower standard was included in each study, which consisted of plots fumigated with methyl bromide (MBr) + Pic 67:33 (v/v) at a rate of 350 lb/acre. Higher rates of MI + Pic 98:2 and 50:50 significantly reduced mixed nutsedge densities and increased relative marketable fruit weight of tomato. Plots fumigated with MBr + Pic were weed-free at the sampling times during both studies. Data from both studies indicated that MI + Pic 98:2 and 50:50 rates of 125 and 200 lb/acre, respectively, consistently provided the highest marketable fruit weights and mixed nutsedge control, which were similar to those obtained in plots treated with MBr + Pic.

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Gary E. Vallad and Bielinski M. Santos

Field studies were conducted in Florida to determine the effect of early shoot pruning on the severity of bacterial spot, and on the growth and yield of different tomato (Solanum lycopersicum) cultivars. Two tomato cultivars, two inoculation regimes of bacterial spot pathogen (Xanthomonas perforans), and three shoot pruning programs were arranged in a split-split plot design. The tomato cultivars were Tygress and Security-28; shoot pruning included none, light, and heavy; and X. perforans treatments consisted of non-inoculated plots and plots inoculated with a suspension of the pathogen. Tomato plant height was not influenced by any of the three factors or their interactions, whereas the disease severity was higher in inoculated plots versus non-inoculated plants. Early extra-large fruit weight was affected by tomato cultivars and the inoculation with the bacterial spot pathogen, but not by pruning programs or the interaction among factors. Tomato plants inoculated with X. perforans reduced their extra-large fruit weight by 31% in comparison with non-inoculated plants. There were no differences on early marketable fruit weight among the combinations of each cultivar and the three pruning programs. All three factors individually influenced the seasonal marketable fruit weight of tomato, with no difference between light-pruned plants and the non-pruned control for seasonal marketable fruit weight, regardless of tomato cultivars. However, heavy pruning did reduce seasonal yields by 10% in comparison with the non-pruned control. These results indicated that light shoot pruning, which is the standard grower practice in Florida, did not improve bacterial spot control or tomato yields of total and extra-large marketable fruit, which might save up to $50/acre in reduced labor costs for Florida tomato growers.

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David H. Suchoff, Christopher C. Gunter and Frank J. Louws

At its most basic, grafting is the replacement of one root system with another containing more desirable traits. Grafting of tomato (Solanum lycopersicum) onto disease-resistant rootstocks is an increasingly popular alternative for managing economically damaging soilborne diseases. Although certain rootstocks have demonstrated ancillary benefits in the form of improved tolerance to edaphic abiotic stress, the mechanisms behind the enhanced stress tolerance are not well understood. Specific traits within root system morphology (RSM), in both field crops and vegetables, can improve growth in conditions under abiotic stress. A greenhouse study was conducted to compare the RSM of 17 commercially available tomato rootstocks and one commercial field cultivar (Florida-47). Plants were grown in containers filled with a mixture of clay-based soil conditioner and pool filter sand (2:1 v/v) and harvested at 2, 3, or 4 weeks after emergence. At harvest, roots were cleaned, scanned, and analyzed with an image analysis system. Data collected included total root length (TRL), average root diameter, specific root length (SRL), and relative diameter class. The main effect of cultivar was significant (P ≤ 0.05) for all response variables and the main effect of harvest date was only significant (P ≤ 0.01) for TRL. ‘RST-106’ rootstock had the longest TRL, whereas ‘Beaufort’ had the shortest. ‘BHN-1088’ had the thickest average root diameter, which was 32% thicker than the thinnest, observed in ‘Beaufort’. SRL in ‘Beaufort’ was 60% larger than ‘BHN-1088’. This study demonstrated that gross differences exist in RSM of tomato rootstocks and that, when grown in a solid porous medium, these differences can be determined using an image analysis system.

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Shichao Wang, Xinlu Bai, Jianbin Zhou and Zhujun Chen

greenhouses in northern China Nutr. Cycl. Agroecosyst. 94 63 72 He, F.F. Chen, Q. Jiang, R.F. Chen, X.P. 2007 Yield and nitrogen balance of greenhouse tomato ( Lycopersicum esculentum Mill.) with conventional and site-specific nitrogen management in northern

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F.M. del Amor, V. Martinez and A. Cerdá

In order to simulate the usage of brackish irrigation water in greenhouse tomato (Lycopersicum esculentum Mill. cv. Daniela) culture in perlite, plants were supplied with nutrient solutions containing 0, 20, 40, and 60 mm NaCl. The three highest salinity treatments were applied at three different plant growth stages, during early vegetative growth [16 days after transplanting, (DAT)], beginning of flowering (36 DAT), and starting fruit development (66 DAT). Salt tolerance of tomato plants increased when the application of salinity was delayed. Salinity significantly decreased size and number of marketable fruits, but increased fruit quality by increasing total soluble solids and sugar content. Leaf and fruit calcium and potassium concentrations were decreased significantly by increasing salinity levels. This was compensated for the accumulation of sodium. Anion accumulation was increased by increasing chloride concentration. These results indicate that it is feasible to use brackish water for growing tomato with minimum yield losses if salt concentration and duration of exposure are carefully monitored.

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M.E. Saltveit

Tomato fruit undergo an orderly series of physiological and morphological changes as they progress from mature-green (MG) to red-ripe. Fruit are commercially harvested at the MG stage, a stage which often encompasses fruit of varying degrees of maturity. The ability to predict the time required for MG fruit to ripen would reduce variability in experiments and could be commercially used to pack fruit that would ripen uniformly. Nuclear magnetic resonance (NMR) imaging can nondestructively measure internal changes associated with plant growth and developmental. In this study, NMR images were taken of freshly harvested tomato fruit (Lycopersicum esculentum cv. Castlemart) at different stages of maturity and ripeness. Measurements were also made of the stage of ripeness, rate of respiration and ethylene production, lycopene and chlorophyll content, density of the pericarp wall, and condition of locular tissue. NMR images showed substantial charges in the pericarp wall and locular tissue during maturation and ripening of tomato fruit. However, it was difficult to objectively evaluate these visual changes with other ripening parameters. For example, increased lightness and graininess of the pericarp wall image was associated with a decrease in wall density; while lightening of the locular image was associated with tissue liquefacation. Use of NMR imaging in studies of tomato fruit ripening will be discussed.

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Samuel J. Dunlop, Marta Camps Arbestain, Peter A. Bishop and Jason J. Wargent

Greenhouse tomato (Lycopersicum esculentum Mill.) producers are urged to reduce their environmental footprint. Here, the suitability of biochar produced from tomato crop green waste as a substrate for soilless, hydroponic tomato production was evaluated. Substrates containing different combinations of biochar (BC) and pine (Pinus radiata D. Don) sawdust (SD) were produced (BC0-SD100, BC25-SD75, BC50-SD50, BC75-SD25, and BC100-SD0) and characterized. The effect of these substrates on tomato growth, yield, and fruit quality was studied. Most of the measured properties of substrates containing biochar were suited to use as a soilless substrate. The electrical conductivity (EC) of substrates containing biochar was initially high (>4.6 mS·cm−1), but was easily reduced to <0.5 mS·cm−1 by rinsing with water before use. The pH of substrates containing biochar was higher than is considered acceptable for tomato production (7.5–9.3) but did not significantly (P < 0.05) affect any plant growth, yield, and fruit quality indicators measured compared with those of plants grown in pine sawdust. The results support the concept of creating a closed loop system whereby biochar produced from tomato crop green waste is used as a substrate for soilless, hydroponic tomato production, providing a sustainable means to support the growth of high-value food crops.