Heirloom tomato varieties are in demand by consumers due to high antioxidant levels. However, these varieties are difficult to produce and are prone to disease. To overcome these problems, heirloom tomatoes may be cultivated in hydroponic systems and grafted onto disease-resistant rootstocks. However, it is unknown if the antioxidant content and capacity are affected by grafting. In this study, heirloom (Black Krim and Green Zebra) and standard (Big Beef) varieties were grafted onto wild type (WT) or productive rootstocks (Arnold and Supernatural). The tomatoes were harvested at maturity, freeze-dried, and ground into a powder. Lycopene was extracted using hexane, and the content was determined spectrophotometrically at 503 nm. The antioxidant capacity of methanol extracts was evaluated by the 2,2′-azino-di[3-ethylbenzthiazoline sulfonsyr]sulphonic acid (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays, whereas the phenolic content was determined using the Folin–Ciocalteu assay. Interestingly, the grafting of Big Beef and Green Zebra onto Supernatural rootstock resulted in an increased antioxidant capacity, as determined by the DPPH assay. Moreover, the phenolic content was changed for Big Beef grafted onto Arnold, and Big Beef and Green Zebra grafted onto Supernatural. Taken together, these results indicate that certain combinations of standard and heirloom tomato varieties and productive rootstocks may influence the antioxidant capacity and phenolic content. These results may be used to guide producers when choosing rootstocks for cultivating hydroponic tomatoes.

Heirloom tomato varieties are in demand by consumers due to high antioxidant levels. However, these varieties are difficult to produce, and are prone to disease and low yield. To overcome these problems, heirloom tomatoes may be grafted onto disease resistant rootstocks. Similarly, hydroponic cultivation have shown to reduce soil‐borne disease and allows year‐round production capabilities. Nevertheless, it is unknown if the antioxidant capacity of hydroponically grown heirloom tomatoes is affected by grafting.To investigate the effects of grafting on hydroponically cultivated tomatoes, heirloom (Black Krim, Green Zebra) and commercial (Big Beef) varieties were grafted onto wild type (WT) or disease resistant rootstocks (Arnold, Supernatural, Maxifort, RST‐04‐105‐T). Tomatoes were harvested at maturity (4.0–6.5 Brix degrees), freeze dried, ground into a powder, and stored at −20°C until further analysis. Extracts were made by incubating 100 mg tomato powder with 1 mL 80% (v/v) methanol, 1 % (v/v) HCl for 2 h while shaking, followed by centrifugation (3000 xg, 5 min) and collection of the supernatant. Antioxidant capacity was determined by the 2,2′‐azino‐di[3‐ethylbenzthiazoline sulfonsyr]sulphonic acid (ABTS) assay. For this, 10 mL of tomato extract was combined with 90 mL of 7 mM ABTS radical (ABTS•), and the absorbance at 734 nm was determined immediately. Trolox was used as a standard and antioxidant capacity was expressed in trolox equivalents (μmol/g dry weight of tomato). Results showed that the antioxidant capacity for Black Krim grafted onto RST‐04‐105‐T was significantly reduced (p<0.05) compared to the WT rootstock. In contrast, Green Zebra and Big Beef grafted onto Arnold, Supernatural, Maxifort, and RST‐04‐105‐T were unchanged compared to the WT. Next, the phenolic content was evaluated using the Folin‐Ciocalteu (FC) assay. In brief, 20 mL tomato extract was combined with 2N Folin reagent and 7.5 % Na2CO3, and the absorbance at 750 nm was immediately determined. Gallic acid was used as a standard and the phenolic content was expressed as gallic acid equivalents (μmol/g dry weight of tomato). The results showed that the phenolic content was significantly (p<0.05) reduced for Green Zebra grafted onto Arnold compared to WT. Black Krim and Big Beef grafted onto Arnold, Supernatural, Maxifort, and RST‐04‐105‐T showed no significant change compared to WT.Taken together, these results indicate that certain combinations of heirloom tomato varieties and disease resistant rootstocks may influence the overall antioxidant capacity and phenolic content as determined by the ABTS and FC assays. Surprisingly, the decrease in antioxidant capacity and phenolic content was not observed for the same tomato and rootstock pair (Black Krim/RST‐04‐105‐T, Green Zebra/Arnold). It is likely, that the RST‐04‐105‐T and Arnold rootstocks effected the content of different types of antioxidants (phenolic versus non‐phenolic) in the two heirloom varieties. These results may be used to guide producers when choosing rootstocks for cultivating hydroponic tomatoes to ensure maintenance of antioxidant content.Support or Funding InformationUSDA IL Speciality Crop GrantThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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