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Growth and yield typically increase when tomato plants are grafted to selected interspecific hybrid rootstocks from which distinctive root system morphologies are envisioned to aid nutrient uptake. We assessed these relationships using a range of exogenous nitrogen (N) supplies under field production conditions. This study analyzed the impact of N on growth, root distribution, N uptake, and N use of determinate ‘Florida 47’ tomato plants grafted onto vigorous, interspecific, hybrid tomato rootstocks ‘Multifort’ and ‘Beaufort’. Six N rates, 56, 112, 168, 224, 280, and 336 kg·ha −1 , were applied to sandy soil in Live Oak, FL, during Spring 2010 and 2011. During both years, the leaf area index, aboveground biomass, and N accumulation (leaf blade, petiole, stem, and fruit) responded quadratically to the increase in N fertilizer rates. Averaged over the two seasons, the aboveground biomass, N accumulation, N use efficiency (NUE), and N uptake efficiency (NUpE) were ≈29%, 31%, 30%, and 33% greater in grafted plants than in nongrafted controls, respectively. More prominent increases occurred in the root length density (RLD) in the uppermost 15 cm of soil; for grafted plants, RLD values in this upper 15-cm layer were significantly greater than those of nongrafted plants during both years with an average increase of 69% over the two seasons. Across all the grafted and nongrafted plants, the RLD decreased along the soil profile, with ≈60% of the total RLD concentrated in the uppermost 0 to 15 cm of the soil layer. These results demonstrated a clear association between enhanced RLD, especially in the upper 15 cm of soil, and improvements in tomato plant growth, N uptake, and N accumulation with grafting onto vigorous rootstocks. 

In this study, the effects of grafting with interspecific hybrid rootstocks on field-grown tomato fruit quality were evaluated over a 2-year period. Fruit quality attributes from determinate ‘Florida 47’ tomato plants grafted onto either ‘Beaufort’ or ‘Multifort’ rootstocks were compared with those from non- and self-grafted controls. Grafted plants had higher fruit yields than non- and self-grafted plants, and increased production of marketable fruit by ≈41%. The increased yield was accompanied by few major differences in nutritional quality attributes measured for these fruit. Although grafting with the interspecific rootstocks led to consistently small, but significant increases of fruit moisture (≈0.6%), flavor attributes such as total titratable acidity (TTA) and the ratio of soluble solids content (SSC) to TTA were not significantly altered. Among the antioxidants evaluated, ascorbic acid concentration was reduced by 22% in fruit from grafted plants, but significant effects were not evident for either total phenolics or antioxidant capacity as assayed by oxygen radical absorbance capacity (ORAC). Levels of carotenoids (lycopene, β-carotene, and lutein) were similar in fruit from grafted plants with hybrid rootstocks compared with non- and self-grafted controls. Overall, the seasonal differences outweighed the grafting effects on fruit quality attributes. This study showed that grafting with interspecific hybrid rootstocks could be an effective horticultural technique for enhancing fruit yield of tomato plants. Despite the modest reduction in ascorbic acid content associated with the use of these rootstocks, grafting did not cause major negative impacts on fruit composition or nutritional quality of fresh-market tomatoes.