Abstract
The combination of increasing costs, climate change, and disease- and pest-related issues present large challenges for the strawberry (Fragaria ×ananassa) industry in the United States. This is especially true for the Southeast, where rain, frost, and a range of foliar, fruit, and soil-borne diseases are prevalent, leading to significant losses every year. Simultaneously, niche winter markets open the opportunity to extend the harvest season, leading to an industry push to use protected culture strawberry production. Tabletop soilless strawberry greenhouse production has the advantage of avoiding soilborne issues while at the same time mitigating weather-related impacts on strawberry yield and quality. The use of long-day cultivars, originally bred for the Central Coast region of California, is currently the industry standard because of desired winter yields. However, short-day cultivars bred for Florida production might also have the potential to produce in winter. In this study, we evaluated the growth, yield, fruit chemistry, and fruit firmness of seven strawberry cultivars that are commonly grown in protected culture in North Carolina: Albion, Brilliance, Camino Real, Fronteras, Monterey, Florida Sensation, and Sweet Charlie. Experiments were conducted in a randomized complete block design in a commercial tabletop greenhouse in eastern North Carolina over two growing seasons (2022–23 and 2023–24). Our results showed that Florida cultivars Brilliance and Florida Sensation produced more consistently yields in winter compared with long-day cultivars Albion and Monterey and produced similar yields over the entire season. ‘Brilliance’ especially showed high fruit firmness across both years, and high sweetness in one of the two years. Additionally, the short-day cultivar Fronteras showed high yields in early spring and could serve as a late-season crop for direct-to-consumer producers. Our study showed that ‘Brilliance’ and ‘Florida Sensation’ could be alternatives to ‘Albion’, and that ‘Monterey’ can be used to produce a winter crop in a soilless tabletop production system in the Southeast.
Strawberries (Fragaria ×ananassa) contribute more than $2 billion to annual farm gate revenue in the United States [US Department of Agriculture (USDA), Economic Research Service 2023]. The majority of commercial strawberry fruit production in the United States relies on the annual hill plasticulture system, with primary production areas located in California and Florida (Holmes 2024; Samtani et al. 2019). Although North Carolina accounts for less than 1% of the national strawberry farm gate value, strawberry production remains vital to local agriculture and the state economy. In 2018, the USDA reported a farm-gate value of $21.4 million for the North Carolina strawberry industry (USDA, National Agricultural Statistics Service 2023). The majority of strawberry farms in North Carolina comprise 1 to 10 acres and primarily sell to local fresh markets, including pick-your-own operations, roadside stands, and farmers’ markets (Hoffmann et al. 2024; McWhirt et al. 2020; Samtani et al. 2019).
The vast majority of strawberry growers in the southeastern United States serve local markets, often reaching higher niche prices for local produce (Hoffmann et al. 2024). However, strawberry growers in the Southeast, like the rest of the United States, face a range of challenges such as increased costs of supplies, land, and labor, increased pests and diseases, and increased frequency and severity of devastating weather events (early spring frosts and heavy precipitation) (Hoffmann et al. 2024; Morton et al. 2017; Samtani et al. 2019). However, at the same time, the demand for local strawberry fruit is increasing (Hinson and Bruchhaus 2008; USDA, Economic Research Service 2023), especially during the winter months (USDA, National Agricultural Statistics Service 2022).
Extending the typical strawberry season (approximately March–June in the Southeast) into more profitable winter markets (November–January) has long been a goal of the regional industry. Methods such as planting long-day cultivars for fall production, using low and high tunnel structures, and using floating row covers have been investigated and are currently used by some farmers as a means of season extension in North Carolina (Ballington et al. 2008; Fernandez and Ballington 2003; Poling and Pattison 2011).
Soilless greenhouse strawberry production is viewed by some in the industry as a potential future production method to reach niche markets at higher price points during the winter months. This notion is supported by consumer acceptance of greenhouse-grown produce (Caputo 2023; Yue et al. 2011). Greenhouse production also avoids climate and disease challenges that come with traditional strawberry production. However, there is a high barrier to entry for growers interested in greenhouse production. Greenhouse production requires significant upfront investment into infrastructure and materials (Savvas and Gruda 2018). In addition, growing strawberries in soilless substrates in a greenhouse requires a different technical skill set than that of traditional production (Sabatino 2020), particularly in areas such as irrigation, fertilization, maintenance, and pest management.
One core component of transitioning to greenhouse strawberry production is understanding cultivar performance in a greenhouse setting. Cultivar availability and consumer acceptance dictate cultivar choices. In the United States, there is little information available regarding cultivar performance in soilless greenhouse environments, thus presenting a challenge to the industry. Currently, growers mostly rely on anecdotal knowledge to make cultivar decisions and mainly use the long-day (everbearing/day-neutral) cultivar Albion. However, because of the comparatively low yield capacity of Albion, other cultivars such as those with low chill requirements or early flowering habits could be more favorable in a greenhouse setting in the Southeast. Therefore, the objective of this 2-year study was to evaluate the performance of seven strawberry cultivars, Albion, Brilliance (Florida Brilliance®), Camino Real, Fronteras, Monterey, Florida Sensation® (Florida127), and Sweet Charlie, in a commercial soilless tabletop greenhouse in eastern North Carolina.
The cultivars Albion, Camino Real, Fronteras, and Monterey were developed at the University of California–Davis (Shaw and Larson 2001, 2004, 2008, 2014). ‘Albion’ and ‘Monterey’ were developed especially for the long days and mild conditions at the California Central Coast. They are long-day cultivars recognized for their capability to continuously produce fruit under long-day conditions. Both cultivars have a large fruit size and firm fruit. ‘Albion’ is typically recognized for its better flavor attributes, whereas ‘Monterey’ has higher yield potential in California production fields (Shaw and Larson 2004, 2008). Camino Real (Shaw and Larson 2001) and Fronteras (Shaw and Larson 2014) are short-day cultivars known for their disease resistance, and they are predominately bred for Southern California production cycles. Both have large firm fruit and are high-yielding. The cultivars Brilliance (Whitaker 2017; Whitaker et al. 2019), Florida Sensation (Whitaker and Chandler 2013), and Sweet Charlie (Howard 1992) were developed for Florida production systems. These are short-day cultivars with low chilling requirements. ‘Brilliance’ and ‘Florida Sensation’ are newer releases from 2017 and 2013, respectively, and have a large fruit size, firm fruit, excellent flavor attributes, and high yield potential in Florida production systems. ‘Sweet Charlie’ was released in 1992 and is known for its early fruit production and consistently sweet fruit, with predominately smaller and softer fruit and lower yield potential (Table 1). We hypothesized that short-day Florida cultivars will produce similar yield in winter compared with the industry standard long-day strawberry cultivars Albion and Monterey and provide similar fruit quality and yields than those of common short-day cultivars.
Strawberry cultivars used for this study.
Materials and Methods
Location and trial design
The experiment was conducted in a randomized complete block design (four replicates per cultivar, 16 plants per replicate) using a commercial strawberry greenhouse in Wilson, NC, USA (lat. 35.708648, long. −78.051865) over the course of two production seasons; the first trial season occurred from 28 Sep 2022 to 22 May 2023 (236 d), and the second trial season occurred from 23 Sep 2023 to 2 May 2024 (222 d). The greenhouse was a house covered with double polyethylene that had roll-up sides for cooling and ventilation as well as fans and heaters available for further environmental controls (Fig. 1). The greenhouse did not feature supplemental lighting, but it did include incandescent lights suitable for night interruption. The plants were grown in raised gutters (tabletop system). Four rows of the greenhouse were used, with each row representing a block, and each block containing all seven cultivars (n = 16 plants per replicate; 64 plants per cultivar).
Planting material
The strawberry cultivars used in this trial were Albion, Brilliance, Camino Real, Fronteras, Monterey, Florida Sensation, and Sweet Charlie (Table 1, Fig. 2). The plants were received as unrooted daughter plants from Balamore Farm Ltd. in Nova Scotia, Canada, and they were propagated in 50-cell trays containing all-purpose media (BM6; Berger, Saint-Modeste, QC, Canada). Daughter plants were kept on a refrigerated truck for 4 d; then, they were rooted outdoors with overhead sprinkler irrigation according to nursery standard practices. After 23 d of establishment, rooted daughter plants were transplanted into the trial (28 Sep 2022 and 23 Sep 2023). Only plants with fully established root balls bearing three to five leaves that fell within a specific crown diameter range were used (Table 2). The rooted daughter plants were transplanted directly into plastic grow bags (Precision Plus Ultra©; Botanicoir Ltd., London, UK). Those bags were located in raised gutters (Haygrove Ltd., UK) that were approximately 1 m from the ground.
Strawberry plug plants were evaluated to determine the crown diameter and leaf number before planting.
Environmental and growing conditions
Temperature conditions were recorded throughout the season (Elitech RC-5 USB Temperature Data Logger; Elitech Technology Inc., San Jose, CA, USA). The temperature loggers were protected from direct solar radiation by aspirated plastic shade covers, and 10 of them were distributed throughout the trial area and maintained at canopy height. To track light intensity, two sensors (HOBO MX2202 Pendant Data Logger; Onset, Bourne, MA, USA) were placed at canopy height. Light intensity was recorded in lux (0–167,731 lx; ±10% typical for direct sunlight); the lux measurements were converted to the photosynthetic photon flux density using the equations described by Thimijan and Heins (1983) and then converted to the daily light integral (CABA 2023). The collaborating grower conducted irrigation, fertility, pest, and disease management according to commercial standards (Tables 3 and 4).
Commercial fertilizer (feed) rates (all nutrients are in mg/L).
Weekly average temperature (°C) and cumulative daily light integral (mol/m2/d) inside the trial area of the commercial greenhouse in Wilson, NC, USA.
Plant growth and development
In both seasons (2022–23 and 2023–24), the crown diameter was measured monthly for the first 5 months of the trial period (September–January) using an electronic caliper (IP54 Electronic Measuring Tool; Housolution, Houston, TX, USA). Initially, the crown diameter of the solitary primary crown was measured. As plants developed multiple crowns, the total number of crowns was recorded, and the diameter of the largest visible crown was measured. At the end of the season, a sample of six plants was collected from each replicate for destructive data collection. The selected plants were cut at the base of the crowns, and the number of crowns and crown diameter of the largest crown were recorded (Table 5). Any fruit, including green fruit, was removed from the plants, and the whole plant was placed in a large brown paper bag. The bags were transported to the North Carolina State University Horticulture Field Laboratory and placed in a large drying oven at 75 °C for 4 d; then, their total foliar dry mass was recorded.
Average diameter of the largest visible crown and observable crown number of seven greenhouse-grown strawberry cultivars sampled monthly from October to January and at the end of the season (EOS) in both seasons (2022–23 and 2023–24).
Additionally, the number of flowers per plant was recorded weekly for 6 weeks following the start of blooming. In the 2022–23 season, the number of flowers was taken from 16 Nov 2022 to 20 Dec 2022; in the 2023–24 season, it was collected from 30 Oct 2023 to 6 Dec 2023. Runners were removed as needed, and their count was recorded during both seasons. The number of leaves and leaf length were recorded once per month during the 2022–23 season only. From Oct 2022 to Feb 2023, the total number of leaves was counted, and the longest leaf was measured from the base of the leaf at the crown to the tip of the central leaflet.
Components of yield
Marketable and nonmarketable fruit were harvested for each replicate once or twice per week, depending on season-specific grower practices. The total mass of the marketable yield and nonmarketable yield was measured in grams using a portable scale (Cruiser Bench Counting Scales-CCT 32; Adam Equipment, Kingston, UK), and the total number of marketable fruits was counted to calculate the average fruit size. Fruits were categorized as marketable or nonmarketable depending on quality factors such as size, shape, color, maturity, and disease presence. Nonmarketable fruits included those less than 10 g, misshapen, over-ripe, under-ripe, or diseased (USDA, Agricultural Marketing Service 2006). During the 2022–23 season, harvesting began during week 48 (2 Dec) of 2022 and continued until week 21 (22 May) of 2023, with a total of 29 harvests. For the 2023–24 season, harvesting began during week 48 (1 Dec) of 2023 and continued until week 18 (2 May) of 2024, with 25 total harvests.
Primary fruit chemistry
In both seasons and for each replicate, up to 10 representative fruits were collected weekly. After removing the calyxes, the fruit was crushed inside sealable plastic bags. Then, the crushed fruit was placed in a freezer at (−20 °C) for 8 d. Following the freezing period, the fruit was allowed to thaw at room temperature for several hours. Once sufficiently thawed, the fruit juice was filtered and collected in beakers. The pH of the juice was measured using a pH meter (PC800 pH/Conductivity Meter; APERA Instruments, Columbus, OH, USA) and collected by submerging the pH probe in the filtered fruit juice. The total soluble solids (TSS; brix) and total acidity (Tacid) were measured using a digital brix-acidity meter (Pocket Brix-Acidity Meter; ATAGO USA Inc., Bellevue, WA, USA). The TSS content was measured by placing two to four drops of the filtered fruit juice on the brix-acidity meter to cover the prism, and the Tacid was measured by diluting 1 mL of the fruit juice in 50 mL of deionized (DI) water and then placing two to four drops of the solution onto the brix-acidity meter to cover the prism.
Fruit firmness
Fruit firmness was evaluated during the 2023–24 season using a texture analyzer (TA.XTPlus Connect, Hamilton, MA, USA) with a 2-mm (TA.52) puncture probe. Up to 10 representative fruits from each replicate were evaluated every week from week 2 (8 Jan) to week 18 (29 Apr) of 2024. Individual fruits were cut longitudinally (from calyx to tip), and one-half of the fruit was placed on the instrument platform with the cut side downward. The fruit was lined up so that the broad section of the fruit was in line with the probe. The force required to puncture the outside of the fruit was recorded as the “first peak force” (FPF), the force required to puncture through the inner layer of the fruit flesh was recorded as the “second peak force” (SPF), and the overall force required to puncture the whole fruit was recorded as the “total force” (TF) (Fig. 3).
Data analysis
Environmental data were managed using Google Sheets (Google, LLC, Mountain View, CA, USA), and graphs in Fig. 4 were created using Microsoft Excel (Microsoft Corporation, Redmond, WA, USA).
During this study, a range of factors led to vastly different seasons. These factors include the difference in the planting dates as well as the harvest season (the 2023–24 season was 3 weeks shorter than that of the 2022–23 season). Moreover, disease pressure was higher in the 2023–24 season, which especially affected ‘Camino Real’. Therefore, we decided to analyze both seasons separately. Yield, plant growth, fruit chemistry, and firmness data (only 2023–24) from each season were analyzed using one-way analyses of variance (ANOVAs) (α ≤ 0.05) performed using Rstudio (Rstudio Desktop version 2023.06.16; Boston, MA, USA). The ANOVAs were followed by a post hoc Tukey’s honestly significant difference test when appropriate (α ≤ 0.05). Fruit firmness data were gathered using a custom macro developed to analyze strawberry firmness. The macro was developed specifically for this project using Exponent software (Texture Technologies Crop, Ltd., Hamilton, MA, USA) in collaboration with Texture Technologies Crop Ltd. (Hamilton, MA, USA).
Results
Yield
For the 2022–23 season, the cultivar with the highest marketable yield at the end of the production period was Florida Sensation, which produced 731.0 g/plant. During weeks 48 and 49 of 2022 (2 and 9 Dec), Monterey produced significantly more marketable fruit than all other cultivars. During week 50 of 2022 (16 Dec), Albion and Monterey both produced more marketable fruit than all other cultivars, and Sweet Charlie produced significantly more fruit than all other cultivars during week 21 of 2023 (22 May) (Table 6, Fig. 4, Supplemental Table 1). All cultivars had low to moderate yields from week 48 of 2022 (9 Dec) to approximately week 11 of 2023 (13 Mar). However, by week 13 of 2023 (27 Mar), the yields began to increase across all cultivars and peaked during weeks 14 to 17 (3–24 Apr). Florida Sensation had the largest average fruit (20.5 g), and all cultivars had significantly larger fruit than Sweet Charlie (11.4 g).
Average marketable yield, nonmarketable yield, and fruit size of seven greenhouse-grown strawberry cultivars per season.
In the 2023–24 season, yields ranged from 277.2 g/plant (‘Camino Real’) to 476.1 g/plant (‘Monterey’). No significant differences were observed in overall yield between the cultivars. However, Albion produced significantly more marketable fruit than all other cultivars during week 48 of 2023 (1 Dec). During weeks 50 and 51 of 2023 (15 and 22 Dec), Brilliance produced significantly more marketable fruit than all other cultivars. All cultivars had low to moderate yields from week 48 of 2023 (1 Dec) to week 8 of 2024 (19 Feb). However, by week 9 of 2024 (26 Feb), marketable yield increased across all cultivars and peaked during week 9 to week 13 of 2024 (25 Mar) (Table 6, Fig. 4, Supplemental Table 1). Fronteras had the largest average fruit (33.4 g) and was significantly larger than all other cultivars except Florida Sensation (30.6 g) (Table 6).
Environmental conditions
Light and temperature.
January was the coldest month during both production seasons, with an average temperatures inside the greenhouse of 9.5 °C ± 0.6 °C in 2023 and 12.5 °C ± 0.5 °C in 2024. The lowest average minimum temperature observed inside the greenhouse during the 2022–23 season was 8 °C (2 and 9 Jan 2023); during the 2023–24 season, it was 9.1 °C (25 Dec 2023). The highest average maximum temperature for the 2022–23 season was 23.6 °C (8 May 2023); during the 2023–24 season, it was 23.1 °C (29 Apr 2024). The highest average daily light integral inside the greenhouse was recorded during week 15 of 2023 (26.8 mol/m2/d) and week 16 of 2024 (25.0 mol/m2/d) (Table 4).
Plant growth and development
Crown diameter and number.
For the 2022–23 season, ‘Monterey’ had the largest average crown diameter initially, with a measurement of 14.2 mm. By the end of the season (EOS), however, ‘Camino Real’ (20.5 mm) had the largest crown diameter, and ‘Sweet Charlie’ (18.5 mm) had the smallest. Additionally, Albion (3.0) had a significantly lower average number of crowns at the EOS than that of all cultivars except Sweet Charlie (3.8) and Brilliance (3.8) (Table 5).
The following season (2023–24) showed a general increase in the average crown diameter across all cultivars (14.3–15.9 mm). Additionally, by the EOS, no significant differences were found between cultivars for the average crown diameter. The EOS crown number data also showed a general increase in the 2023–24 season; the range in the first season was 3.0 to 4.5, and that in the second season was 3.5 to 5.6. In general, over both years, crown numbers doubled from the beginning to the EOS for most cultivars (Table 5).
Leaf number and length.
Leaf number and length were assessed in the 2022–23 season. ‘Fronteras’ (11.9), ‘Monterey’ (11.9), and ‘Florida Sensation’ (12.3) had significantly more leaves than ‘Albion’ (9.0) and ‘Camino Real’ (9.9). ‘Fronteras’ had the highest average leaf length (14.8 cm), which was significantly longer than that of the leaves of ‘Camino Real’, ‘Brilliance’, ‘Albion’, and ‘Sweet Charlie’ (Table 7).
Average leaf number and length, flower number, and foliar dry mass of seven greenhouse-grown strawberry cultivars.
Early-season flower assessment.
Flower numbers were assessed weekly for a total of 5 weeks following the start of blooming (approximately November–December). During the early season in 2022–23, Monterey and Sweet Charlie produced the most flowers of all the cultivars, with both averaging 1.47 flowers per plant. ‘Camino Real’, produced the least number of flowers, with an average of only 0.68 flowers per plant (Table 7). In the 2023–24 early season, Brilliance (1.14) produced significantly more flowers per plant on average than every other cultivar, whereas ‘Fronteras’ had significantly fewer flowers on average (0.08 per plant) than all other cultivars (Table 7).
Foliar dry mass.
At the EOS of 2022–23, ‘Fronteras’, ‘Monterey’, and ‘Camino Real’ had significantly higher foliar dry mass than ‘Albion’. At the EOS 2023–24, ‘Florida Sensation’, ‘Monterey’, and ‘Brilliance’ had significantly higher foliar dry mass than ‘Albion’ and ‘Camino Real’ (Table 7).
Postharvest quality
Fruit chemistry.
During the 2022–23 season, the average TSS/Tacid ratio ranged from 12.6 (‘Albion’ and ‘Brilliance’) to 18.0 (‘Sweet Charlie’). Most cultivars were similar, with TSS/Tacid ratios of approximately 12.6 to 14.7, except for Sweet Charlie, which exhibited a significantly higher ratio. During the 2023–24 season, the ratios ranged from 23.4 (‘Camino Real’) to 30.7 (‘Florida Sensation’). Sweet Charlie and Florida Sensation had the highest TSS/Tacid ratio, 29.5 and 30.7 respectively, which were significantly higher than those of the other cultivars.
In 2022–23, Sweet Charlie had a significantly higher average pH (3.8) than that of all other cultivars. The average Tacid was similar for most cultivars; however, Albion (0.60%) and Monterey (0.58%) had significantly higher average Tacid than that of the other cultivars (Table 8). Sweet Charlie (8.0) had significantly higher TSS overall than that of most cultivars (Table 8). The TSS varied over the season for all cultivars (Supplemental Table 2). During week 9 of 2023 (27 Feb), ‘Camino Real’ had a significantly lower TSS (4.8) than that of all other cultivars. ‘Florida Sensation’ had its highest average TSS (9.5) during week 7 of 2023 (13 Feb). ‘Albion’ had its highest average TSS (9.5) during week 12 of 2023 (20 Mar). Sweet Charlie had its highest average TSS (9.6) during week 16 of 2023 (17 Apr), which was significantly higher than that of all other cultivars that week. ‘Camino Real’ had its highest average TSS (8.8) during week 17 of 2023 (24 Apr), and ‘Brilliance’, ‘Fronteras’, and ‘Monterey’ had their highest average TSS (8.2, 8.5, and 9.2, respectively) during week 19 of 2023 (8 May) (Supplemental Table 2).
Average primary fruit chemistry: pH, total acidity (Tacid), and total soluble solids (TSS) of seven greenhouse-grown strawberry cultivars over two production seasons.
In 2023–24, no differences in pH were detected, but the Tacid varied among the cultivars and was highest for Camino Real (0.41%). Fronteras had a significantly lower average overall TSS (7.1) than that of all cultivars (Table 8). The TSS varied across cultivars and over the season. ‘Monterey’ (10.3) and ‘Albion’ (10.6) had peak TSS during weeks 2 and 3 of 2024, respectively (8 and 15 Jan). ‘Fronteras’ had its highest TSS (8.4) during week 6 of 2024 (5 Feb). ‘Brilliance’ had its highest TSS (10.6) during week 10 of 2024 (4 Mar), and ‘Camino Real’ (11.3) peaked during week 13 of 2024 (25 Mar). ‘Florida Sensation’ and ‘Sweet Charlie’ (11.1 and 10.3) both had peak TSS during week 14 of 2024 (1 Apr) (Supplemental Table 2).
Fruit firmness.
For the 2023–24 season as a whole, Brilliance had a significantly higher average FPF (149.4 g), average SPF (210.5 g), and average TF (641.3 g/s) than those of all other cultivars (Table 9). Notably, Sweet Charlie was the only cultivar with a lower average SPF (86.9 g) than FPF (89.0 g), showing that the fruit has relatively soft internal flesh. Additionally, fruit firmness varied over the season for all cultivars (Supplemental Tables 3–5).
Average firmness of seven greenhouse-grown strawberry cultivars for the 2023–24 season.
The TF of all cultivars generally declined over the season. ‘Albion’ (658.7 g/s), ‘Brilliance’ (865.9 g/s), ‘Camino Real’ (792.7 g/s), ‘Fronteras’ (829.9 g/s), and ‘Florida Sensation’ (729.6 g/s) experienced their highest average TF during week 3 of 2024 (15 Jan). The average TF of ‘Sweet Charlie’ peaked (368.5 g/s) during week 4 of 2024 (22 Jan), and that of ‘Monterey’ peaked (619.4 g/s) during week 9 of 2024 (26 Feb). Sweet Charlie tended to have the lowest average TF, which was significantly lower than that of all cultivars during weeks 7 (12 Feb), 12 (18 Mar), and 14 (1 Apr) of 2024 (Supplemental Table 3).
The results of the FPF varied over the season for all cultivars, but all showed the highest FPF during the month of January. ‘Monterey’ had its highest FPF (166.7 g) during week 2 of 2024 (8 Jan). ‘Camino Real’ (219.3 g) and ‘Fronteras’ (138.1 g) exhibited their highest FPF in week 3 of 2024 (15 Jan). During the following week, ‘Albion’ (167.8 g), ‘Brilliance’ (229.2 g), ‘Florida Sensation’ (159.7 g), and ‘Sweet Charlie’ (126.5 g) all had their highest FPF (Supplemental Table 4).
The SPF results differed from the patterns of the FPF; however, the results varied over the course of the season, and several cultivars showed their highest SPF toward the end of the season. ‘Albion’ (210.4 g), ‘Camino Real’ (235.8 g) and ‘Monterey’ (178.4 g) had their highest SPF during week 3 of 2024 (15 Jan). ‘Sweet Charlie’ (112.3 g) had its highest SPF during week 6 of 2024 (5 Feb), and the SPF of ‘Fronteras’ (240.3 g) peaked during week 14 of 2024 (1 Apr). ‘Brilliance’ (309.9 g) and ‘Florida Sensation’ (207.9 g) both had the highest SPF toward the end of the season during week 17 of 2024 (22 Apr) (Supplemental Table 5).
Discussion
Tabletop strawberry production comprise a very small percentage of the overall strawberry industry in the United States, which is mostly in open-field annual hill plasticulture (Hoffmann et al. 2024; Samtani et al. 2019). Therefore, the evaluation of strawberry cultivars in US greenhouse production systems is not very well-explored. However, because flower formation in strawberry is influenced by both temperature and photoperiod (Durner et al. 1984), strawberry cultivars generally perform differently in protected soilless systems when compared with the traditional open-field plasticulture systems. Research of the strawberry yield and quality performance in such protected systems is essential to determine the suitability of specific cultivars for strawberry greenhouse production (Garcia and Kubota 2017).
Yield potential
In the Southeast, the strawberry cultivar Albion has emerged as the main cultivar for greenhouse and tabletop cultivation; however, in California, the cultivar Monterey is used in the few nonpreparatory tabletop operations. Those cultivars are used because of the consistent yield potential under warmer temperatures experienced in greenhouse and the mostly long days experienced in those areas (Samtani et al. 2019). Albion and Monterey were the only two long-day cultivars used in this study. Both cultivars showed yield in winter months, which is consistent with growers’ anecdotal experience. Guan et al. (2022) evaluated ‘San Andreas’ and ‘Sweet Ann’ as well as ‘Albion’ in high tunnels in Indiana and found that ‘San Andreas’ had a higher yield potential than ‘Albion’. Similar findings were found in high tunnels in North Carolina (Gu et al. 2017). However, high tunnel and greenhouse growers in the Southeast have moved on from ‘San Andreas’ to ‘Albion’ or Florida genetics under high tunnels and specifically ‘Albion’ in greenhouses. This notion, however, is not supported in our study. Albion and Monterey showed no significant differences in marketable yield when compared with other evaluated cultivars.
Florida short-day strawberry cultivars may offer advantages to greenhouse growers as well. For example, Gu et al. (2017) found that when using a high tunnel production system in North Carolina, the cultivars Florida Radiance and Winterstar showed high yield potential. Guan et al. (2022) reported that Florida-bred strawberry cultivars reached high yield potential. Short-day genetics can also lead to higher yields in general and better overall flavor qualities compared with those of long-day cultivars (Lewers et al. 2020). However, our findings of the overall yield of the cultivars Camino Real, Fronteras, Brilliance, and Florida Sensation revealed no significant differences over both years, with the exception of Camino Real in season 2023–24, because of the high disease incidence.
However, yield patterns between the cultivars varied significantly in both seasons. ‘Florida Sensation’ and ‘Brilliance’ provided consistent yields in winter in both seasons, whereas ‘Monterey’ and ‘Albion’ only peaked in one of the two seasons in winter. This clearly demonstrated the potential of ‘Brilliance’ and ‘Florida Sensation’ for potential North Caroline greenhouse tabletop production and cannot be understated. The other Florida cultivar Sweet Charlie also showed a similar pattern. However, because of significantly lower fruit size and less favorable fruit quality and firmness compared with those of all other cultivars, Sweet Charlie would not be recommended for greenhouse production in North Carolina.
The yields of all cultivars generally peaked in Apr 2023 and Mar 2024. Understanding peak production patterns is important for marketing purposes and could be used to strategically ensure a continuous supply of fruit throughout the season. This strategy is supported by studies such as those by Amyotte and Samtani (2023), which emphasized the importance of cultivar selection to extending the harvest season. However, based on the yield patterns in our study, valuable alternatives to long-day cultivars for North Carolina greenhouse growers might be Brillance and Florida Sensation.
A direct comparison of greenhouse production to open-field production is difficult. However, according to the data from the North Carolina State University Strawberry Breeding Program (Fernandez 2023), ‘Albion’ produced more fruit during the greenhouse season (in grams per plant) than during a “typical” field production season. The cultivars Fronteras, Monterey, Florida Sensation, and Sweet Charlie generally had similar yields in both the greenhouse and field. No outdoor yield data were available for ‘Brilliance’. However, yields can differ widely between grower and season, and the data set cited here may only provide noncomplete insights into the yield potential of those cultivars in North Carolina. However, the typical field strawberry harvest window in North Carolina ranges (depending on the region) from early April to early-to-mid June. The strawberry harvest from November through March can only be achieved in protected culture systems in North Carolina.
Plant growth
Leaf number and size can be important factors for determining a strawberry plant’s capacity to support fruit development (Carey et al. 2009). This was not supported by our results that showed that ‘Fronteras’, ‘Monterey’, and ‘Florida Sensation’ had the highest leaf counts, whereas ‘Albion’ had the fewest leaves. However, over yields did not differ significantly between the cultivars. Leaf length followed a similar trend, with ‘Fronteras’ having the longest leaves and ‘Albion’ having the shortest, thus indicating that ‘Fronteras’ had a more full and vigorous growth habit than ‘Albion’. Although we did not find a strong correlation between leaf number or leaf length and overall yield (Supplemental Fig. 1), these differences in leaf characteristics highlight the variability of plant morphology between cultivars that can be important for production in terms of spray penetration and ease of harvest (Carey et al. 2009; Gu et al. 2017). These traits can also be important for breeding programs that seek to develop cultivars adapted to greenhouse and controlled environment production.
During the 2022–23 season, Camino Real, Fronteras, and Monterey had the highest foliar dry mass; however, in the 2023–24 season, only Monterey remained in the top three cultivars. Moreover, ‘Camino Real’ had the lowest foliar dry mass in 2023–24, and this was largely because of significant disease issues affecting the plant health and viability of this cultivar.
Despite ‘Sweet Charlie’ having a higher average number of early-season flowers, the overall yield was not higher in early production because of the low fruit size. Similarly, Brilliance had a moderate number of early-season flowers and low early yields in the 2022–23 season, but it produced significant early flowers and yields the following season, showing that flower to fruit development may be cultivar-dependent and environment-dependent (Menzel 2021; Samad et al. 2021).
Hanson et al. (2006) reported that crown diameter and number are positively correlated with fruit yield in several strawberry cultivars grown in high tunnels. Our results did not align with this because we did not find a strong correlation between yield and crown diameter (Supplemental Fig. 2). For instance, Brilliance had significantly more crowns than other cultivars in the 2023–24 season, but not significantly more yield. Whereas in the 2022–23 season, both the crown number and average yield were lower among all the cultivars.
Strawberry fruit quality and firmness
Strawberry flavor is a complex fruit trait and consists of sugars, acids (amino and organic), and aromatic compounds. Sugars are an important component of flavor and can vary over time and based on cultivar (Haynes 2024). The Tacid is a measurement of nonvolatile organic acids in the sample. Previously, acceptable TSS and Tacid were 7.0% and 0.8%, respectively (Kader 1999). However, recently consumer demands dictate that the minimum TSS should be raised to 9.0%, and that the Tacid should remain approximately 0.8% (Haynes 2024).
Our postharvest chemistry results emphasize the variability in fruit quality among the different cultivars and the impact of seasonal changes on these quality parameters. For the 2022–23 season, Sweet Charlie had the highest average TSS of 8.0%, and that of other cultivars ranged from 6.1% (Brilliance) to 7.4% (Albion). The following season, all TSS levels were generally higher, and ‘Albion’ had the highest (at 9.4%) on average. The TSS is a crucial quality parameter because it correlates with perceived sweetness and overall fruit flavor, thus significantly affecting the marketability of strawberries, especially in North Carolina, where most strawberries are sold in local fresh markets (Hoffmann et al. 2024). In the 2022–23 season, several of the cultivars (Brilliance, Camino Real, and Fronteras) did not meet the 7.0% TSS standard for consumer acceptability. However, in the following season, the majority of cultivars were at or above the newly suggested TSS standard of 9.0%, and all of the cultivars were above the 7.0% TSS threshold.
Higher acid levels contribute to the tartness of the fruit, which influences the overall flavor balance (Kader 1999). The Tacid was variable across cultivars and seasons. In general, Tacid was higher in the first season (2022–23), ranging from 0.47% to 0.60%; however, it ranged from 0.26% to 0.41% in the second season (2023–24). Strawberry fruit pH varied the least among the components we measured, with the average pH ranging from 3.5 to 3.8 across cultivars and seasons, with most at approximately 3.65. The pH is an important component of flavor because acidity is inversely related to perceived sweetness of strawberries (Cordenunsi et al. 2003). However, there were almost no significant differences in pH across the cultivars and seasons in this study.
The 2023–24 season exhibited higher postharvest fruit quality traits, such as higher TSS and lower Tacid, compared with those during the previous season. These differences can be attributed to the differing environmental factors. The cooler temperatures during the second half of the 2023–24 season may have contributed to the higher TSS and lower Tacid of the fruit. Temperature conditions during ripening can affect the postharvest quality of strawberry fruit (Taghavi et al. 2019; USDA, Agricultural Marketing Service 2006). Additionally, studies have shown that higher light intensity results in higher acid levels in the strawberry fruit, in alignment with our results that showed that acidity levels were higher in the 2022-23 season when the light intensity in the greenhouse was comparatively higher (Taghavi et al. 2019). The combination of these factors likely resulted in the observed differences in postharvest fruit quality traits between the two seasons.
Fruit firmness is a characteristic that is important to marketability. Studies have shown that harvesting at peak firmness enhances shelf life and consumer satisfaction (Kader 1999; Vicente et al. 2009). Brilliance consistently exhibited high firmness metrics compared with that of other cultivars, aligning with the study of Whitaker et al. (2019), who reported moderate firmness for Brilliance. Conversely, ‘Sweet Charlie’ consistently showed low firmness values. This variation in fruit firmness has practical implications for growers because understanding the firmness characteristics of different cultivars can guide selection for specific market needs. For example, cultivars with higher firmness, like Brilliance, may be preferred for markets requiring a longer shelf life, whereas softer cultivars like Sweet Charlie may be more suitable for local markets with quicker turnover between harvest and consumption. However, Sweet Charlie specifically had lower fruit size compared with that of all other cultivars and would not be recommended for greenhouse strawberry production in North Carolina.
Conclusions
We compared the yield performance, fruit quality, and firmness of seven strawberry cultivars in a commercial North Carolina tabletop greenhouse operation for two seasons. We found that ‘Brilliance’ and ‘Florida Sensation’ provided the most consistent yield in winter over both seasons and could be valuable alternatives for North Carolina greenhouse growers compared with the industry standards ‘Albion’ and ‘Monterey’. ‘Brilliance’ exhibited the highest fruit firmness, best flavor attributes, and overall yield similar to that of ‘Albion’ and ‘Monterey’. Moreover, the short-day cultivar Fronteras showed consistently high yield potential in the late season, indicating the potential value for a direct-to-consumer market. However, ‘Fronteras’ had very low sugar levels in one of the two seasons. Moreover, the cultivars Camino Real and Sweet Charlie are not recommended for greenhouse tabletop production because of the inferior size and flavor.
References Cited
Amyotte B, Samtani JB. 2023. New directions for strawberry research in the 2020s. Int J Fruit Sci. 23(1):278–291. https://doi.org/10.1080/15538362.2023.2274894.
Ballington JR, Poling B, Olive K. 2008. Day-neutral strawberry production for season extension in the midsouth. HortScience. 43(7):1982–1986. https://doi.org/10.21273/HORTSCI.43.7.1982.
CABA Tech. 2023. How to use PPFD measurements to hit DLI targets. https://cabatech.com/how-to-use-ppfd-measurements-to-hit-dli-targets/. [accessed 2 Jun 2024].
Caputo T. 2023. Demand for greenhouse produce fuels sales surge, innovation. https://www.thepacker.com/news/industry/demand-greenhouse-produce-fuels-sales-surge-innovation. [accessed 1 Jul 2024].
Carey EE, Jett LW, Lamont WJ, Nennich TT, Orzolek MD, Williams KA. 2009. Horticultural crop production in high tunnels in the United States: A snapshot. HortTechnology. 19(1):37–43. https://doi.org/10.21273/HORTTECH.19.1.37.
Cordenunsi BR, Nascimento JRO, Lajolo FM. 2003. Physico-chemical changes related to quality of five strawberry fruit cultivars during cool-storage. Food Chem. 83(2):167–173. https://doi.org/10.1016/S0308-8146(03)00059-1.
Durner EF, Barden JA, Himelrick DG, Poling EB. 1984. Photoperiod and temperature effects on flower and runner development in day-neutral, junebearing, and everbearing strawberries. J Am Soc Hortic Sci. 109(3):396–400. https://doi.org/10.21273/JASHS.109.3.396.
Fernandez GE, Ballington JR. 2003. Double cropping of strawberries in an annual system using conditioned plug plants and high tunnels. Acta Hortic. 614:547–552. https://doi.org/10.17660/ActaHortic.2003.614.81.
Fernandez GE. 2023. Replicated cultivar and selection breeding trials. https://strawberries.ces.ncsu.edu/straberry-breeding-progam/replicated-cultivar-and-selection-breeding-trials/. [accessed 1 Jul 2024].
Garcia K, Kubota C. 2017. Flowering responses of North American strawberry cultivars. Acta Hortic. 1156:483–490. https://doi.org/10.17660/ActaHortic.2017.1156.71.
Gu S, Wenjing G, Beck J. 2017. Strawberry cultivar evaluation under high-tunnel and organic management in North Carolina. HortTechnology. 27(1):84–92. https://doi.org/10.21273/HORTTECH03559-16.
Guan W, Haseman D, Ingwell L, Egel DS. 2022. Strawberry cultivar evaluation for fall-planted high tunnel system. HortTechnology. 32(6):542–551. https://doi.org/10.21273/HORTTECH05103-22.
Hanson P, Hancock JF, Flore JA. 2006. Crown and flower development in June-bearing strawberry cultivars in a high tunnel environment. HortScience. 41(4):1147–1150.
Haynes B. 2024. Characterization of fruit composition of North Carolina strawberry germplasm (MS Diss). North Carolina State University, Raleigh, NC, USA.
Hinson RA, Bruchhaus MN. 2008. Consumer preferences for locally produced strawberries. J Food Dist Res. 39(3):56–66. https://doi.org/10.22004/ag.econ.55984.
Hoffmann M, McWhirt A, Samtani J, Moore C, Schnabel G, Tregeagle D, Dankbar H, Fernandez G, Simmons C, Perkins-Veazie P, Poling B, Lockwood D, Flanagan R, Eure E, Holmes K, Melanson R, Hicks K, Cato A, Gu S. 2024. Southern Regional Strawberry Plasticulture Production Guide. NC State Extension Publications. https://content.ces.ncsu.edu/southern-regional-strawberry-plasticulture-production-guide. [accessed 28 May 2024].
Holmes G. 2024. The California strawberry industry: Current trends and future prospects. Int J Fruit Sci. 24(1):115–129. https://doi.org/10.1080/15538362.2024.2342900.
Howard CM. 1992. Strawberry plant called ‘Sweet Charlie’. US Patent PP 8729. https://patents.justia.com/patent/PP8729.
Kader AA. 1999. Fruit maturity, ripening, and quality relationships. Acta Hortic. 485:203–208. https://doi.org/10.17660/ActaHortic.1999.485.27.
Lewers KS, Newell MJ, Park E, Luo Y. 2020. Consumer preference and physiochemical analyses of fresh strawberries from ten cultivars. Int J Fruit Sci. 20(Suppl 2):733–756. https://doi.org/10.1080/15538362.2020.1768617.
McWhirt A, Fernandez G, Schroeder-Moreno M, Hoffmann M. 2020. Sustainable practices for plasticulture strawberry production in the South. NC State Extension Publications. https://content.ces.ncsu.edu/sustainable-practices-for-plasticulture-strawberry-production-in-the-south. [accessed 28 May 2024].
Menzel C. 2021. Higher temperatures decrease fruit size in strawberry growing in subtropics. Horticulturae. 7(2):34. https://doi.org/10.3390/horticulturae7020034.
Morton LW, Peres N, Fraisse C, Gleason M. 2017. Climate, weather and strawberries. Sociology Technical Report 1047. Department of Sociology, Iowa State University, Ames, IA, USA.
Poling B, Pattison J. 2011. Increasing high tunnel strawberry productivity in the late fall and early winter with day neutral strawberries and the new Florida short day cv. Radiance. Preliminary Report on Albion Strawberry in Piedmont, NC, USA.
Sabatino L. 2020. Increasing sustainability of growing media constituents and stand-alone substrates in soilless culture systems—an editorial. Agronomy. 10(9):1384. https://doi.org/10.3390/agronomy10091384.
Samad S, Butare D, Marttila S, Sønsteby A, Khalil S. 2021. Effects of temperature and photoperiod on the flower potential in everbearing strawberry as evaluated by meristem dissection. Horticulturae. 7(11):484. https://doi.org/10.3390/horticulturae7110484.
Samtani JB, Rom CR, Friedrich H, Fennimore SA, Finn CE, Petran A, Wallace RW, Pritts MP, Fernandez G, Chase CA, Kubota C, Bergefurd B. 2019. The status and future of the strawberry industry in the United States. HortTechnology. 29(1):11–24. https://doi.org/10.21273/HORTTECH04135-18.
Savvas D, Gruda N. 2018. Application of soilless culture technologies in the modern greenhouse industry – a review. Europ J Hortic Sci. 83(5):280–293. https://doi.org/10.17660/eJHS.2018/83.5.2.
Shaw DL, Larson KD. 2001. Strawberry plant named ‘Camino Real’. US Patent 20020152524. https://patents.justia.com/patent/20020152524.
Shaw DL, Larson KD. 2004. Strawberry plant named ‘Albion’. US Patent 20050172374. https://patents.justia.com/patent/20050172374.
Shaw DL, Larson KD. 2008. Strawberry plant named ‘Monterey’. US Patent PP19767. https://patents.justia.com/patent/PP19767.
Shaw DL, Larson KD. 2014. Strawberry plant named ‘Fronteras’. US Patent 20150230374. https://patents.justia.com/patent/20150230374.
Taghavi T, Siddiqui R, Rutto LK. 2019. The effect of preharvest factors on fruit and nutritional quality in strawberry. IntechOpen. https://10.5772/intechopen.84619.
Thimijan RW, Heins RD. 1983. Photometric, radiometric, and quantum light units of measure: A review of procedures for interconversion. HortScience. 18(6):818–822. https://doi.org/10.21273/HORTSCI.18.6.818.
US Department of Agriculture, Agricultural Marketing Service. 2006. United States standards for grades of strawberries. https://www.ams.usda.gov/grades-standards/strawberries-grades-and-standards. [accessed 28 May 2024].
US Department of Agriculture, Economic Research Service. 2023. The changing landscape of US strawberry and blueberry markets: Production, trade, and challenges from 2000 to 2020. Report no. EIB–257. https://doi.org/10.32747/2023.8134359.ers.
US Department of Agriculture, National Agricultural Statistics Service. 2022. Noncitrus fruits and nuts 2021 summary. https://www.nass.usda.gov/Publications/Todays_Reports/reports/ncit0522.pdf. [accessed 2 Jun 2024].
US Department of Agriculture, National Agricultural Statistics Service. 2023. 2023 North Carolina agricultural statistics. https://www.nass.usda.gov/Statistics_by_State/North_Carolina/Publications/Annual_Statistical_Bulletin/AgStat/NCAgStatBook.pdf. [accessed 28 May 2024].
Vicente AR, Manganaris GA, Ortiz CM, Sozzi GO, Crisosto CH. 2009. Nutritional quality of fruits and vegetables, p 57–106. In: Florkowski WJ, Shewfelt RL, Brueckner B, Prussia SE (eds). Postharvest handling: A systems approach. Elsevier, Amsterdam, Netherlands.
Whitaker VM. 2017. Strawberry plant named ‘Florida Brilliance’. US Patent 20190124811. https://patents.justia.com/patent/20190124811.
Whitaker VM, Chandler CK. 2013. Strawberry plant named ‘Florida Sensation’. US Patent 20140359905. https://patents.justia.com/patent/20140359905.
Whitaker VM, Peres NA, Osorio LF, Fan Z, do Nascimento Nunes MC, Plotto A, Sims CA. 2019. ‘Florida Brilliance’ Strawberry. HortScience. 54(11):2073–2077. https://doi.org/10.21273/HORTSCI14327-19.
Yue C, Dennis JH, Behe BK, Hall CR, Campbell BL, Lopez RG. 2011. Investigating consumer preference for organic, local, or sustainable plants. HortScience. 46(4):610–615. https://doi.org/10.21273/HORTSCI.46.4.610.