Abstract
Grafting tomatoes with vigorous rootstocks can be used to increase yield in high tunnels without significant soilborne disease pressure. However, evidence suggests that grafting with high-yielding rootstocks could compromise the accumulation of primary and secondary metabolites. ‘Tasti Lee’ is a hybrid tomato that is bred to have a superior fresh-eating quality and higher lycopene content. The objective of this experiment was to investigate the yield and fruit quality impacts of grafting ‘Tasti Lee’ with rootstocks with ranging vigor and typical yield performance in high tunnels. Nongrafted ‘Tasti-Lee’ and ‘Tasti-Lee’ scion grafted onto ‘Maxifort’, ‘DRO141TX’, ‘Fortamino’, ‘Estamino’, and ‘RST-04-106-T’ rootstocks were trialed in a high tunnel in Kansas for three consecutive growing seasons (2018–20). The trials were arranged in a randomized complete block design with four replications. Total yield, marketable yield, average fruit size, and distribution of fruit size classes were assessed. Red ripe tomato fruit were harvested to determine the soluble solids content, titratable acidity, lycopene content, vitamin C content, antioxidant capacity, and fruit firmness. ‘Maxifort’, ‘DRO141TX’, ‘Estamino’, and ‘Fortamino’ significantly increased marketable yield (kg/plant) by 31.5% to 47.0% more than nongrafted plants. In contrast, ‘RST-04-106-T’ did not lend any significant yield benefit. Regardless of the rootstock, grafting increased the marketable average fruit weight by 20 g. Grafting did not have significant effects on any of the fruit quality attributes assessed. However, the soluble solids content of fruit from plants grafted to ‘RST-04-106-T’ was 10% higher (P < 0.05) than that grafted to ‘Maxifort’, indicating that rootstock genotype can influence this quality trait. Our findings suggest that growers can graft the tomato ‘Tasti-Lee’ with select vigorous rootstocks to increase marketable yield without sacrificing fruit quality for high tunnel production.
Consumers are increasingly dissatisfied with the flavor of modern tomato (Solanum lycopersicum L.) cultivars and are willing to pay higher prices for better-flavored or locally grown specialty tomatoes (Jordan, 2007; Tieman et al., 2017). In response, tomato breeding programs have focused more on breeding for improved flavor and nutrition (Baldwin et al., 2015). Tasti-Lee is a determinate, fresh market cultivar that is professionally marketed by Bejo Seeds and sold as a premium tomato (Scott et al., 2008). The tomato has deep red pigment and up to 40% more lycopene content than other fresh market cultivars because it contains the crimson (ogc) gene (Scott et al., 2008). The cultivar is harvested vine-ripe and has improved flavor, a long shelf life, and high consumer acceptance (Cantliffe et al., 2009; Scott et al., 2008).
Vegetable grafting is a compatible practice that can improve tomato crop performance in high tunnels. In the central United States, growers predominantly cultivate tomatoes in high tunnels. Vigorous rootstocks often have been used to increase marketable tomato yield in central U.S. high tunnel cultivation, where little to no disease pressure is evident (Lang et al., 2020; Loewen et al., 2020; Masterson et al., 2016; Meyer et al., 2021) ‘Tasti-Lee’ could offer high tunnel growers a high-value and unique product for marketing to consumers, restaurants, and other regional markets. Previous high tunnel trials in Kansas have found that grafting ‘Tasti-Lee’ to the rootstock ‘Maxifort’ can increase marketable yields by 59.5% more than nongrafted plants (Loewen et al., 2021).
In the literature, there are wide-ranging results concerning the tomato fruit quality impact of grafting. Some graft combinations have caused reductions in the soluble solids content (SSC) (Casals et al., 2018; Mauro et al., 2020b; Milenković et al., 2020; Turhan et al., 2011), vitamin C (Koleška et al., 2018; Nicoletto et al., 2013; Turhan et al., 2011), antioxidant concentrations (Moreno et al., 2019; Nicoletto et al., 2013; Riga et al., 2016), and increases in titratable acidity (TA) (Khah et al., 2006; Turhan et al., 2011). Scion × rootstock × environment interactions also influence fruit quality traits (Albacete et al., 2015; Cohen et al., 2007; Djidonou et al., 2020), thus highlighting the importance of conducting production system-specific rootstock trials for scions of interest.
Additionally, the degree of vigor afforded by the rootstocks may influence changes in fruit composition (Mauro et al., 2020a; Mauro et al., 2020b). For instance, the antioxidant capacity of ‘BHN 589’ tomato fruit increased when grafted to the rootstock ‘RST-04-106-T’, but the rootstock provided no yield benefit in high tunnel cultivation. In contrast, the higher-yielding rootstock ‘Maxifort’ produced fruit with antioxidant capacity comparable to nongrafted plants (Meyer et al., 2021). The rootstocks selected for this study were chosen because their typical yield performance ranges.
‘Maxifort’ is an interspecific rootstock classified as having high vegetative vigor, and it often improves yield in high tunnels with low disease pressure (Loewen et al., 2020; Masterson et al., 2016; Meyer et al., 2021). ‘DRO141TX’ is also classified as a highly vigorous rootstock by seed companies, but it has less often been reported in the literature. Similarly, ‘Estamino’ is described as having generative vigor by adding more energy to fruit production than vegetative production. Lang et al. (2020) found that ‘DRO141TX’ and ‘Estamino’ performed similarly to ‘Maxifort’ in high-tunnel tomato production with the scion ‘BHN 589’. ‘Fortamino’ is even less studied, but it is recommended for early vegetative vigor and increasing the number of flowers per truss and average fruit size. Preliminary data observed in Kansas showed that it increases yield with ‘BHN 589’ scion (Rivard, unpublished data). ‘RST-04-106-T’ was included because it typically does not provide yield benefits in high tunnel production, where little disease pressure is present (Lang and Nair, 2019; Meyer et al., 2021).
Tasti-Lee is explicitly marketed for its premium flavor and nutritional quality; therefore, it is critical to understand how grafting with vigorous rootstocks affects this cultivar of tomato. More specifically, the objectives of this study were to report the effect of grafting the scion ‘Tasti-Lee’ to typically high-yielding and low-yielding rootstocks for high tunnel production in regard to yield and fruit size, investigate the effects of these rootstocks on fruit quality, and determine if rootstocks impact flavor and nutritional quality parameters differently.
Materials and Methods
High tunnel trials were conducted in the same high tunnel in 2018, 2019, and 2020, at the Kansas State University Olathe Horticulture Research and Extension Center. The trials were arranged in a randomized complete block design with four replications, and the arrangement of the plots were re-randomized each year. The treatments consisted of nongrafted ‘Tasti-Lee’ as well as five rootstock treatments with ‘Tasti-Lee’ scion grafted onto ‘Maxifort’ (De Ruiter, St. Louis, MO), ‘DRO-141-TX’ (De Ruiter), ‘RST-04-106-T’ (DP Seeds, Yuma, AZ), ‘Fortamino’ (Enza Zaden, Salinas, CA), and ‘Esatmino’ (Enza Zaden) rootstocks.
Transplant production.
The grafted and nongrafted plants were propagated in a greenhouse at the Olathe Horticulture Research and Extension Center using the splice/tube grafting method outlined by Rivard and Louws (2011). The seeds of rootstocks and the scion were sown in a commercial germination mix (Fafard Germinating Mix; Sun Gro Horticulture, Agawam, MA) and then transplanted into 50-cell propagation trays filled with professional growing mix (Metro-Mix 852; Sun Gro Hort Canada Ltd., Seba Beach, AB Canada). Approximately 25 d after seeding, when the plants had two to four true leaves, they were splice-grafted and joined using silicon clips (Hydro-Gardens, Colorado Springs, CO). The plants were transferred to a healing chamber in the greenhouse covered with 4-mil polyethylene film and a 55% shadecloth. The chambers had cool mist humidifiers to maintain high relative humidity. After 7 to 10 d, the plants were removed from the healing chambers and grown in the greenhouse for at least 14 d before being transplanted into the high tunnel.
High tunnel trial design and management.
The 3-year trial occurred in a 9.1-m-wide × 19.5-m-long moveable high tunnel (Rimol Greenhouse Systems; Hooksett, NH) at the Olathe Horticulture Research and Extension Center located in Johnson County, KS (38.884347, −94.993426). The movable tunnel has three set positions on a 200-foot track; each year, the high tunnel was in a different position. The soil type was chase silt loam. In 2019 and 2020, a spring lettuce crop preceded the tomato trial. The lettuce was harvested on 5 June 2019 and 20 May 2020. Four 16.5-m-long beds oriented north and south within the tunnel were the experimental replications and blocks. The tomatoes were transplanted into the high tunnel on 25 May 2018, 24 June 2019, and 5 June 2020. Each rootstock treatment was randomly assigned to one of six plots in each bed. Each plot had five plants, and the in-row spacing was 18 inches. Standard high tunnel cultural practices were followed, including a raised bed plasticulture system with drip irrigation. Watering was dependent on weather, but it typically occurred three times weekly, with watering events lasting between 45 and 120 min. Nutrients were supplied with a custom-blended granular preplant fertilizer (31N–16P–16K) at 56 kg⋅ha−1 N and two fertigation events with potassium nitrate at 11.2 kg⋅ha−1 each. The between-row weeds were managed using black fabric mulch, and the tomatoes were trained using a stake and weave vertical trellis system. The main pest pressure was from tomato fruitworms and hornworms. When worms were observed, Bacillus thuringiensis was sprayed biweekly until the end of the growing season.
Harvesting and yield.
Based on the U.S. Department of Agriculture maturity standards, all fruit from the breaker stage to the red maturity stage were harvested each week (U.S. Department of Agriculture, 1991). In 2018, this occurred from 2 July to 18 Oct. Fruit was harvested from 26 July to 1 Oct. 2019, and from 20 June to 16 Oct. 2020. There were 12 harvests in 2018, 5 harvests in 2019, and 11 harvests in 2020. The fruit from each plot were separated by marketability, which was determined by being the lack of large cracks, pest damage, rot, and blossom end rot. Marketable fruit were sorted according to the U.S. Department of Agriculture size classes (small, medium, large, and extra-large) (U.S. Department of Agriculture, 1991). The various sizes of marketable fruit and the unmarketable fruit were counted and weighed. All fruit larger than 5 cm were harvested, counted, and weighed on the last harvest day of the season.
Fruit sampling for quality assessment.
Fruit from one harvest in 2018 and 2019 and two harvests in 2020 were used for fruit quality analyses. All fruit quality evaluations were conducted at the Kansas State University Postharvest Physiology Laboratory at the Kansas State University Olathe Campus.
Tomatoes at the red maturity stage from each experimental unit were harvested for quality analysis. The harvest dates for the fruit quality analysis were 18 Oct. 2018, 1 Oct. 2019, 31 Aug. 2020, and 8 Sept. 2020. On the day of harvest, the fruit was transported in an air-conditioned vehicle to the Postharvest Physiology Laboratory (≈20 min drive). To ensure the fruit were at a homogenous maturity stage, external color data were collected on each fruit by taking two measurements at opposite 45-degree angles on the blossom end with a color meter (A5 Chroma-Meter; Minolta Co. Ltd., Osaka, Japan). All fruit had an average “a*” value of 25.4 ± 1.7 and an a*/b* of 0.9 ± 0.8. The a* represents the degree of redness, and b* represents the degree of yellowness. The a*/b* ratio increases as tomatoes ripen and can be used as an indicator of the maturity stage (Batu, 2004; Brajovic et al., 2012).
Reagents and chemicals.
All chemicals and reagents were purchased from Thermo Fisher Scientific (Waltham, MA). The lycopene standard reference material was purchased from Millipore Sigma (Burlington, MA).
Fruit firmness and organoleptic quality.
In 2020 only, fruit firmness of five tomatoes from each experimental unit was measured using a texture analyzer (TA-58 TA.XT.plus; Texture Technologies Corp., Scarsdale, NY). Using a TA-30 75-mm-diameter flat plate texture analyzer, the peak force needed for 2-mm compression deformation was measured in grams. Firmness (N/mm) values were calculated as the average slope in the deformation curve divided by the peak force (g) as described by Jackman et al. (1990).
After firmness was measured, the fruit was cut into quarters from the stem end to the blossom end. One-quarter from each of the five fruit per replication was blended, and 20 g of the puree was centrifuged. The hydrophilic supernatant was used for the determination of TA and SSC. Approximately 2 g of the blended tissue was homogenized with 20 mL of 6% metaphosphoric acid with 2 N acetic acid solution and frozen at −20 °C until the analysis of ascorbic acid (AsA). The remaining portions of the tomatoes were frozen at −20 °C until the analysis of lycopene and antioxidant capacity.
For TA, 5 mL of the tomato supernatant was mixed with 45 mL of deionized water and measured with an automated titrator (862 Food/Beverage Compact titrosampler; Metrohm, Herisau, Switzerland). The results are reported as the citric acid equivalent (%). The SSC of the samples was measured by placing a drop of the hydrophilic tomato fraction on a hand-held digital refractometer (AR200; Reichert, Depew, NY). The results are reported as °Brix.
AsA determination.
Determination of AsA was based on the method by Klimczak and Gliszczynska-Wiglo (2015). The previously frozen extracts were thawed, vortexed, and centrifuged. The supernatant was further diluted with 6% metaphosphoric acid/2 N acetic acid solution (1 supernatant:4 solution) and filtered through a 1-mL, 96-well, 0.22-μm filter plate (AcroPrep; Pall Co., Port Washington, NY) into a 2-mL, 96-well plate (SKU: 186002482, Waters Co., Milford, MA). Samples were read using an ultra-performance liquid chromatographer (Waters Aquity UPLC, Waters Co.) equipped with a photodiode array detector and a BEH C18 column (Aquity, Waters Co). Each well was injected in triplicate with 5 μL of sample volume. The mobile phases consisted of 5 mm potassium phosphate monobasic (KH2PO4), pH 2.65, with 0.1% of formic acid (mobile phase A) and methanol with 0.1% of formic acid (mobile phase B). At a flow rate of 0.2 mL/min, the solvent management was a linear gradient starting with 5% A, with an increase to 15% A over the course of 1 min, then to 35% A over the course of 1 min, and then a return to the initial conditions over the course of the next 4 min. An external 5-point analytical AsA standard curve was created on the day of analysis with 10% meta-phosphoric acid solution; it ranged from 2.5 to 5 μg⋅mL−1. The standard curve was used for the quantification of chromatograms read at 245 nm. Ascorbic acid content is reported as mg AsA per 100 g of fresh weight.
Lycopene determination.
The remaining frozen tomato samples were lyophilized in a freeze dryer before the lycopene and antioxidant analyses (Harvest Right, Salt Lake City, UT). The extraction and ultra-performance liquid chromatography/ultraviolet detection method for the determination of lycopene was based on a method by Maurer et al. (2014), with slight modification. The light was reduced during sample extraction and when handling standard reference material to avoid carotenoid degradation. Finely ground lyophilized tissue (0.05 g) was weighed in 30-mL polypropylene copolymer extraction tubes; 6 mL of acetone/methanol (2:1, volume/volume; 0.5% butylated hydroxytoluene) and 3 mL of hexane with 0.5% butylated hydroxytoluene were added to the tubes, vortexed, and sonicated in an ice bath for 20 min. To promote phase separation, 5 mL of 1 M sodium chloride solution was added. The sample extract was centrifuged at 1800 rpm for 10 min at 4 °C. An aliquot from the hexane layer was collected and filtered with 0.22-um, 13-mm PTFE syringe filters (VWR, Wayne, PA) into 2-mL amber sample vials (Waters Co.) for analysis. Lycopene standard reference material was dissolved in hexane (0.5% butylated hydroxytoluene) and used to make an external standard curve ranging from 1.875 ug⋅mL−1 to 60 ug⋅mL−1.
The samples were read using ultra-performance liquid chromatography (Aquity, Waters Co.) with a reverse-phase hollow structural section C18 2.1- × 100-mm, 1.8-µm column (Waters Co.) and a photodiode array detector. The mobile phase A consisted of 75:23:2 acetonitrile/water/hexane (volume/volume/volume; 0.1% acetic acid volume/volume). Mobile phase B was 90:80:2 acetonitrile/butanol/hexane (volume/volume/volume; 0.1% acetic acid volume/volume). At a flow rate of 0.5 mL⋅min−1, the solvent gradient consisted of a 0.5-min hold on 100% A, a 1-min gradient to 20% A, and a 0.1-min shift to 0% A, followed by 100% A until 13.5 min. Absorbance was recorded at 450 and samples were quantified with the lycopene standard curve and expressed as lycopene equivalent as μg⋅g−1 dry weight (DW).
Antioxidant capacity analysis.
The sample preparation and extraction of antioxidants was based on a method by Ou et al. (2002). Briefly, 0.25 g of lyophilized tissue was added to 10 mL of acetone/water (50:50, volume/volume) extraction solution. The solution was shaken at 400 rpm on an orbital shaker for 1 hour; then, it was centrifuged (10,000 rpm, 20 min, 4 °C). The extract was further diluted by adding 1120 μl of acetone/water (50:50, volume/volume) to 80 μl of the extract. The antioxidant capacity was analyzed using the ferric-reducing ability of plasma (FRAP) method (Benzie and Strain, 1996). Then, 50 μl of the diluted sample extract was added to the 180-μl FRAP reagent (ferric chloride/tripyridyltriazine/acetate buffer), and each sample was pipetted into a 96-well microplate in triplicate. Antioxidants in the sample extract reduced the ferric chloride/2,4,6-Tris(2-pyridyl)-s-triazine (tripyridyltriazine) reagent and changed the solution color to blue. The plate was read with a spectrophotometer at 593 nm (Synergy H1; BioTek, Winooski, VT). A 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox) positive control curve ranging from 10 to 60 µmol⋅L−1 was used for quantification, and the final results were expressed as µmol Trolox equivalents per gram of DW.
Statistical analysis.
All data analyses were performed with statistical software (SAS version 9.4; SAS, Cary, NC). The PROC GLIMMIX model with DDFM=KR in the MODEL statement was used for all analyses. The yield parameters were determined on a per-plant basis for analysis and presentation of the data. For the yield-related response variables, the fixed effects of rootstock treatments, year, and a treatment × year interaction were modeled with block and treatment × block effects in the RANDOM statement. The least significant difference was used for mean separation at a significance level of P ≤ 0.05.
For the fruit quality data, the two harvests in 2020 were combined because there were no significant rootstock × harvest interactions. The postharvest data were analyzed as described for the yield data, but the SSC/TA ratio and lycopene content were natural log-transformed to improve data normality. All data were back-transformed for presentation. Tukey’s honest significant difference test was used for post hoc mean separation of postharvest data; significance was considered when P ≤ 0.05.
Results
Yield.
Table 1 provides the probability values of the effects of rootstock treatments and year on yield parameters. There was a significant effect of year on the total and marketable yield parameter, but there were no significant interactions between year and rootstock. Therefore, the three years were combined, and the main effect of grafting was considered. All of the rootstocks except for ‘RST-04-106-T’ increased the total (P ≤ 0.01) and marketable (P ≤ 0.05) weights of fruit harvested compared with the nongrafted plants (Table 2). When compared with the nongrafted plants, the remaining four rootstocks increased the marketable yield by 31.6% to 47.2% (Table 2). Grafting with ‘RST-04-106-T’ did not increase marketable yield, but it was also not lower than the yield achieved by ‘Maxifort’, ‘DRO141TX’, and ‘Estamino’ rootstocks. The number of marketable fruit was not impacted by grafting, but the total number of fruit harvested significantly increased when ‘Tasti-Lee’ was grafted to ‘Maxifort’, ‘Fortamino’, and ‘Estamino’ (P ≤ 0.01) when compared with the nongrafted control.
Probability values of yield parameters from the overall ANOVA F-test of main effects (rootstock treatments and production year) and rootstock treatment × year interaction.
Tomato fruit yield of nongrafted and grafted ‘Tasti-Lee’ tomatoes grown in a high tunnel at the Olathe Horticulture Research and Extension Center in 2018, 2019, and 2020.
All rootstocks increased the average weight of marketable (P ≤ 0.01) and total fruit (P ≤ 0.001). The marketable fruit from grafted plants was, on average, 20 g heavier than fruit from nongrafted ‘Tasti-Lee’. More extra-large fruit were harvested from grafted plants than nongrafted plants, except for the rootstock ‘RST-04-106-T’ (P ≤ 0.01; Table 3). Plants grafted to ‘Maxifort’ produced more than twice as many extra-large fruits as the nongrafted plants.
Tomato size distribution of marketable fruit harvest from grafted and nongrafted ‘Tasti-Lee’ tomato grown in a high tunnel at the Olathe Horticulture Research and Extension Center in 2018, 2019, and 2020.
Fruit quality.
For fruit quality measurements, there were no significant interactions between year × rootstock; therefore, only the effect of rootstocks is considered. There was significant year-to-year variation for all fruit quality criterium assessed except for antioxidant capacity (FRAP). Rootstock treatments only led to significant effects on SSC (P ≤ 0.05).
The SSC of ‘Tasti-Lee’ tomatoes from all treatments ranged from 4.31 °Brix to 4.67 °Brix (Table 4). The tomatoes grafted to ‘RST-04-106-T’ had the highest SSC (4.67 °Brix) and were greater than those grafted to ‘Maxifort’, which had the lowest SSC (4.31 °Brix) (P ≤ 0.05). The rootstock treatments had SSC similar to that of the nongrafted ‘Tasti-Lee’ tomatoes. There were no significant differences in the TA or the SSC/TA of fruit from any rootstock treatment.
Organoleptic fruit quality soluble solids content (SSC), titratable acidity (TA), and the SSC/TA ratio of ‘Tasti-Lee’ tomatoes harvested during 2018, 2019, and 2020.
The antioxidant capacity (FRAP), lycopene content, and ascorbic acid content were similar across all treatments (Table 5). Numerically, the rootstock ‘RST-04-106-T’ had the highest mean lycopene content of 842.55 μg⋅g−1 DW, and nongrafted plants had the lowest at 534.81 μg⋅g−1 DW. Fruit firmness was only assessed in 2020 across two harvests. There was no significant effect of harvest days; therefore, the treatment means across both harvests are provided in Fig. 1. There were no significant treatment effects on fruit firmness (N/mm), and the average firmness value was 19.1 ± 4.7 N/mm.
Average fruit firmness of fruit harvested at the red maturity stage in 2020. Bars represent the least significant means for each rootstock treatment group and error bars represent the sem. Firmness was measured with a TA-58 TA.XT.plus texture analyzer and a flat plate.
Citation: HortScience 57, 10; 10.21273/HORTSCI16634-22
Nutritional fruit quality: lycopene, FRAP, and ascorbic acid content of ‘Tasti-Lee’ tomatoes harvested during 2018, 2019, and 2020.
Discussion
This trial aimed to determine the effects on ‘Tasti-Lee’ tomato yield from grafting to five different rootstocks. The overall yield achieved during this experiment was lower than that previously reported for grafted and nongrafted ‘Tasti-Lee’ tomatoes in high tunnel trials conducted in a different high tunnel structure at the same location (Loewen et al., 2020; Oxley et al., 2015). Loewen et al. (2020) ound that marketable yield for nongrafted ‘Tasti-Lee’ plants ranged from 5.7 to 6.7 kg/plant, whereas the average in this trial was 2.7 kg/plant. Loewen et al. (2020) also reported that marketable yield increased by 59.5% when grafted to ‘Maxifort’, whereas the increase was 34.2% in this trial. Although cultivation practices were similar, the trials were performed within a different high tunnel structure and experienced varied environmental and soil conditions and pest pressure, which could result in the discrepancy. Additionally, the plants were transplanted into the high tunnels an average of 45 d later compared with the previously mentioned trials, which likely accounts for the reduced overall yield. Later planting dates can result in higher temperatures during initial flowering, which interfere with proper pollination and can reduce yield (Rogers and Wszelaki, 2012).
There was a significant year-to-year variation in yield, but the rootstocks performed similarly relative to each year. The rootstocks ‘Maxifort’, ‘DRO141TX’, ‘Fortamino’, and ‘Estamino’ increased marketable yield compared with the nongrafted ‘Tasti-Lee’ plants. ‘Maxifort’ is a popular rootstock in the United States and has often been found to increase marketable yield in protected culture systems without significant pathogen pressure (Djidonou et al., 2017; Lang et al., 2020; Masterson et al., 2016; Meyer et al., 2021). Similar to our findings, Lang et al. (2020) observed that ‘Estamino’ and ‘DRO141TX’ performed similarly to ‘Maxifort’ and increased marketable yield in high tunnel cultivation with the scion ‘BHN 589’. ‘Fortamino’ has been less studied, but it achieved the highest marketable yield increases (47.2%) in this trial, although they were not significantly different from ‘Maxifort’. This same graft combination (‘Tasti-Lee’/‘Fortamino’) was also recently trialed in open-field production without disease pressure in North Carolina, where it increased marketable yield by 22% and performed similarly to the rootstock, ‘Beaufort’ (Ingram, 2020). The results of this experiment add to the evidence that ‘RST-04-106-T’ does not improve marketable yield in high tunnels without significant disease pressure (Lang and Nair, 2019; Lang et al., 2020; Meyer et al., 2021).
Tasti-Lee typically produces smaller tomatoes compared with other beefsteak tomato cultivars, and increasing the average fruit size could also be desired from a marketing perspective. During our experiment, we measured average fruit weight as an indicator of size and also sorted marketable fruit into U.S. Department of Agriculture size grades. Increases in the average fruit weight and size are the most consistent effects of vigorous, interspecific rootstocks (Kyriacou et al., 2017). During our investigation, all the rootstocks increased the average fruit weight of ’Tasti-Lee’ tomatoes by 9% to 15%. The number of extra-large fruit also increased from all the rootstock other than ‘RST-04-106-T’. This degree of fruit weight increase is consistent with the results of other vigorous rootstocks/scion combinations in open-field production (Djidonou et al., 2013, 2016), high tunnel production (Lang et al., 2020; Masterson et al., 2016; Meyer et al., 2021), and greenhouse production (Mauro et al., 2020b; Rahmatian et al., 2014). Loewen et al. (2020) found that grafting ‘Tasti-Lee’ to the rootstock ‘Maxifort’ increased the average fruit weight by an average of 33% in a similar high tunnel system, but this effect was not significant. Ingram (2020) reported that ‘Tasti-Lee’ grafted to the rootstock ‘Beaufort’ also increased the number of extra-large fruit harvested in open-field production. A possible mechanism of rootstock induced increases in fruit size could be related to an increased flow of assimilates and water during the fruit expansion phase (Djidonou et al., 2013). In general, increases in yield—either through increased fruit number and/or increased fruit size—of grafted plants grown without disease pressure are attributed to inherent vigor and improved nutrient and water uptake by vigorous root systems (Djidonou et al., 2013).
This trial was the first to investigate rootstock effects on the fruit quality of high tunnel-grown ‘Tasti-Lee’ tomatoes. The fruit SSC and TA found during this experiment are lower than those previously reported for open-field production of ‘Tasti-Lee’ (Ingram, 2020; Scott et al., 2008) and higher than those reported for winter-grown greenhouse ‘Tasti-Lee’ production (Cantliffe et al., 2009). However, the SSC/TA ratio of the nongrafted tomatoes in this experiment agrees with those assessed over multiple seasons in Florida (Scott et al., 2008).
We found that grafting onto a rootstock did not cause a significant difference in the SSC, TA, or SSC/TA ratio, or in firmness of the fruit compared with the nongrafted controls. These organoleptic parameters are essential for tomato taste and consumer acceptance (Causse et al., 2010). Therefore, our data suggest that the taste was not significantly impacted because of grafting. Considering that ‘Tasti-Lee’ is marketed for improved flavor, changes in these organoleptic parameters are important to understand. This cultivar is characteristically firm; therefore, it is beneficial that the vigorous rootstocks did not compromise this trait, despite increasing the average fruit size and weight (Scott et al., 2008). Future research should include consumer sensory analyses to investigate any perceived flavor or preference changes from grafting ‘Tasti-Lee’ or other improved-flavor scions.
The effects of rootstocks on fruit SSC and TA differ from those reported by Ingram (2020), who found that grafting ‘Tasti-Lee’ to ‘Beaufort’, ‘Arnold’, and ‘Shield’ significantly reduced fruit SSC by 4% to 8%, and that grafting to ‘Beaufort’ and ‘Shield’ significantly reduced the TA of the fruit. However, the numerical reductions in SSC from grafting to ‘Maxifort’, ‘Fortamino’, and ‘DRO141TX’ during our experiment were similar and ranged from 3% to 5%. Vigorous rootstocks have often been reported to decrease SSC by an average of 9% to 13% in a variety of production systems (Al-Harbi et al., 2017; Casals et al., 2018; Mauro et al., 2020b; Milenković et al., 2020; Moreno et al., 2019; Pogonyi et al., 2005; Turhan et al., 2011). Increases in the TA of tomatoes have also been attributed to grafting with vigorous rootstocks such as ‘Maxifort’ (Krumbein and Schwarz, 2013; Meyer et al., 2021). Others have found no effect on fruit TA when grafting with this same rootstock (Djidonou et al., 2017; Lang et al., 2020), similar to our findings. These findings suggest that TA is highly subject to scion × rootstock interactions.
The mechanisms of fruit composition effects from vigorous rootstocks are not clearly understood, but increased vegetative and root biomass could act as additional assimilate sinks in competition with the fruit (Martínez-Ballesta et al., 2010; Mauro et al., 2020a; Mauro et al., 2020b). Improved water uptake from vigorous rootstocks may result in an increased flow of water to the fruit during fruit expansion, which could increase fruit size and dilute the SSC (Mauro et al., 2020b; Turhan et al., 2011). Increases in fruit load may also reduce assimilate partitioning into individual fruits. Interestingly, plants grafted to ‘RST-04-106-T’ produced mature red fruit with the highest SSC among all treatments and nongrafted plants and was significantly higher than that of fruit from plants grafted to ‘Maxifort’. ‘RST-04-106-T’ was the only rootstock to not significantly increase yield, and it had lower fruit numbers compared with the other rootstocks assessed. Lang et al. (2020) also reported that ‘RST-04-106-T’ significantly increased the SSC of the scion ‘BHN 589’ above higher-yielding vigorous rootstocks, including ‘Maxifort’, ‘Estamino’, and ‘DRO141TX’ during one year of the trial. These results support the hypothesis that differences in SSC between rootstocks could be related to the overall vegetative vigor and/or fruit load afforded by the rootstock. Alternatively, changes could be attributable to direct changes in transcriptional processes of sugar metabolism from the ‘RST-04-106-T’ rootstock. Watermelon grafted to bottle gourd rootstocks have been found to have differently expressed genes related to sugar metabolism and sugar transport (Aslam et al., 2020).
The organoleptic quality of tomatoes is often subject to environmental variation (Panthee et al., 2012), and changes attributed to the harvest period (Di Gioia et al., 2010; Djidonou et al., 2017) or year (Barrett et al., 2012; Lang et al., 2020) are often more significant than rootstock effects. It is important to note that the fruit in this study was only sampled one or two times each year toward the end of the season, when there was sufficient red fruit. Future investigations would benefit from more sampling periods or larger plots to confirm our results regarding the rootstock effects on flavor quality of ‘Tasti-Lee’ tomatoes.
Rootstocks did not significantly affect the lycopene content, AsA content, and antioxidant capacity of ‘Tasti-Lee’ tomatoes, and seasonal variations led to greater concentration differences in these nutritional parameters. There were no significant variations in these functional compounds between fruit from the high-yielding rootstock treatments (‘Maxifort’, ‘Fortamino’, ‘Estamino’, ‘DRO-141-TX’) and the lower-yielding ‘RST-04-106-T’ treatment. Therefore, these compounds were not influenced by overall rootstock production performance. Grafting-induced changes in functional compounds are often highly dependent on scion × rootstock combination and interactions with the environment. Vigorous rootstocks have unaffected lycopene (Djidonou et al., 2016, 2017; Khah et al., 2006) and decreased lycopene content (Gajc-Wolska et al., 2014; Helyes et al., 2009; Krumbein and Schwarz, 2013). In open-field production, grafting ‘Tasti-Lee’ to the rootstocks ‘Beaufort’ and ‘Shield’ significantly reduced lycopene by 6%, whereas the rootstock ‘Arnold’ was comparable to nongrafted plants (Ingram, 2020). The numerical differences in lycopene content between treatments were greater in this trial, but not statistically significant, which likely indicates the greater variability within each rootstock treatment found in this trial in comparison with the results reported by Ingram (2020). All the rootstocks we trialed had, on average, greater lycopene content than the nongrafted plants; therefore, we can suggest that grafting did not compromise the lycopene content of this high-lycopene cultivar.
Previously, the lower-yielding ‘RST-04-106-T’ rootstock was found to significantly increase FRAP over the course of 2 years with the scion ‘BHN-589’ grown using high tunnel cultivation (Meyer et al., 2021). However, we did not observe any benefit or reduction in antioxidant capacity with ‘Tasti-Lee’ as the scion. Reductions in AsA are also common when grafting to vigorous, interspecific rootstocks such as ‘Maxifort’ (Di Gioia et al., 2010; Ilić et al., 2020) and ‘Beaufort’ (Turhan et al., 2011), but the use of vigorous rootstocks did not limit the accumulation of ‘Tasti-Lee’ tomatoes. The ability of this cultivar to maintain its nutritional content when it is grafted to vigorous rootstocks makes it an attractive option for this production system.
Conclusion
As grafting technology is deployed in high tunnel and open-field systems across the United States, growers need research-based information to determine if this strategy will work not only for their production systems but also for their customers. ‘Tasti-Lee’ is marketed as a tomato with good flavor and nutritional quality, which could be affected by the use of vigorous rootstocks. The results of our trials suggest that grafting with select vigorous rootstocks increased the marketable yield of ‘Tasti-Lee’ tomatoes grown in a high tunnel without compromising quality. The SSC of tomatoes from the plants grafted to the ‘RST-04-106-T’ rootstock was significantly greater than that of those grafted to ‘Maxifort’, suggesting rootstocks can differently influence fruit composition of this scion. Because ‘Tasti-Lee’ can be sold at a premium price, an economic analysis of a high tunnel grafting system with this scion would be useful for growers to make informed decisions as they implement integrated technologies such as vigorous rootstocks and high-lycopene scions.
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