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Hort Series #243

Principal Investigators: Jonathan R. Schultheis, Professor and Extension Specialist, Department of Horticultural Science, NC State University; Stuart W. Michel, Research Technician, Department of Horticultural Science, NC State University; Brandon K. Parker, Research Associate, Department of Horticultural Science, NC State University; Baker E. Stickley, Research Assistant, Department of Horticultural Science, NC State University; Andrew P. Pfefferkorn, Research Technician Support, Department of Horticultural Science, NC State University.

        View or print the pdf of this report

Acknowledgements

We gratefully acknowledge the assistance of Hunter Barrier (Superintendent) and Wesley Hairre (Horticulture Supervisor), Horticultural Crops Research Station, Clinton, NC, as well as the personnel at the research station for their help in establishing, maintaining, and harvesting the 2023 cultigen evaluation study. We want to acknowledge summer employees Lia Hunt and Daphne Meyer for their assistance with this study. The cooperation and support of BASF/Nunhems, Bayer/Seminis, Enza Zaden, Hazera, HM Clause, Origene Seeds, Known You Seed, Sakata Seed Company, Seedway, Syngenta, and U.S. Seedless were also appreciated. We also want to thank Joy Smith for performing the statistical analysis and aiding in the interpretation of the data collected from this study.

Disclaimer

This publication presents data from the standard size triploid watermelon cultigen evaluation study conducted during 2023. Information in this report is believed to be reliable but should not be relied upon as a sole source of information. Limited accompanying detail is included but excludes some pertinent information, which may aid interpretation.

Introduction

In 2022, an estimated 93,200 acres of watermelon was harvested in the U.S. (aei.ag). Total acreage is down since 2021 and has been on a decline since 2016; acreage is 17% less in 2022 than it was in 2016. The southern regions of the U.S. are the primary watermelon producers with Florida leading production at 36% of U.S. acreage followed by Georgia (29%) and Texas (25%) as of 2022. Last year, watermelons accounted for 14.1 pounds of the 22.1 pounds of melons made available to U.S. consumers, making up the majority of that share; cantaloupe made up 5.3 pounds and honeydew made up 1.6 pounds per U.S. consumer (ers.usda.gov). Most of the watermelons consumed in the U.S. are grown domestically, but imports have increased to almost 40% over the past 5 years with most imports coming from Mexico.

North Carolina is ranked 5th in total watermelon acres harvested in the U.S. at 7,600 acres as of 2022. This harvested acreage equated to a value of 56 million USD (nass.usda.gov). Watermelon production in North Carolina is down by 1,700 acres from the 9,300 acres that were harvested in 2021 (NCAgStatBook2022). Typical planting dates in North Carolina range from 25 March to 10 May and typical harvest dates range from 1 July to 10 September.

In 2023, Dr. Schultheis and the Cultural Management Program in the Horticulture Department at NC State University conducted an evaluation of 32 standard size triploid (seedless) cultigens and 1 diploid (seeded) watermelon cultigen from 11 seed companies at the Horticultural Crops Research Station in Clinton, NC. The watermelon entries were evaluated for yield and quality characteristics such as soluble solids (sweetness or Brix), color, firmness, and hollow heart. The methods, results, and representative photos from the study are presented below (Figures 2-34).

Materials and Methods

Sowing and Field Preparations

Once all seeds were received from participating companies, they were planted into 72-cell poly trays to grow transplants (Hummert Int.; Earth City, MO). The watermelons were sown on 23 March 2023. The trays of sown seeds were placed in a germination room for 24-48 hours. Temperature in the germination room was kept between 90-95°F and humidity was kept between 85-90%. The planting medium used was a ‘fine germinating mix’, a commercial soilless mix (SunGro, Agawam, MA). After germination, transplants were moved to a greenhouse set to 85°F and hand watered twice daily. Due to a heater malfunction, transplants were moved to a larger greenhouse after approximately 1 week and remained there for 4 weeks until transplanting. The seedlings were fertilized at least once a week with 20-10-20 water soluble fertilizer at a rate of 200-250 ppm.

The field planting site was located at the Horticultural Crops Research Station in Clinton, NC. The watermelons were transplanted in the field blocks S1 and S2; a Lynchburg sandy loam soil type. Telone II (12 gal/ac) was applied broadcast to the entire study area on 1 March 2023 for weed and nematode control. K-Mag fertilizer (0-0-22-22-11Mg) at 150 lb/ac was applied pre-plant on 3 April 2023 and NPK fertilizer (10-10-10) at 500 lb/ac was applied on 12 April 2023. Black polyethylene plastic (1.25 mil thick, high density plastic film, 54 inches wide; TriEast Ag Group, Inc., Clinton, NC) was laid on 18 April 2023.

Transplanting and Vine Training

The triploid (seedless) watermelon transplants and the diploid (seedless) transplant were established in the field on 10 May 2023. Plot size for the watermelons was 1 row, 10 plants per row, 25 feet long with alleys of 10 feet between plots. Row middles were 10 feet and in-row spacing was 2.5 feet. Plots with missing plants were replaced 1 week after transplanting to achieve 100% plant stand. ‘SP-7’ and ‘Wingman’ (4 plants/plot) were used as the pollenizer plants in this study. ‘SP-7’ pollenizers were planted after triploid plants 1 and 7 while ‘Wingman’ pollenizers were planted after triploid plants 4 and 10 in each plot. Once vines had grown over the plastic mulch, they were gently turned/trained back into the plot each week. This aided with harvest by avoiding mixing cultigens and reducing vine damage at harvest.

Fertilizer and Pest Management

A total of 50 units/ac N, 50 units/ac P, 83 units/ac K, 33 units/ac S, and 16.5 units/ac Mg were applied broadcast (pre-plant) to the entire study area. Drip tape (NETAFIM, 12 in spacing, 0.24 gph; NETAFIM, Tel Aviv, Israel) was installed beneath the black plastic mulch to fertigate the crop throughout the growing season. Liquid fertilizer with 4-0-8 analysis was applied through drip tape fertigation 11 times at rates of 25, 20, or 15 gal/ac. Cumulative totals, preplant and through the drip tape, of applied fertilizer nutrients were: 166 units/ac N, 50 units/ac P, 314 units/ac K, 33 units/ac S, and 16.5 units/ac Mg.

Herbicides (Table 1), insecticides (Table 2), and fungicides (Table 3) were applied as needed and as directed by the label for that crop (2023 North Carolina Agricultural Chemicals Manual). Different products were rotated to avoid potential development of resistance.

Weather

The weather was generally favorable for the duration of the study (Figure 1). Temperatures in the spring were cool until around June when the averages rose to around 80 °F and conditions remained hot throughout the summer. We had a few periods of heavy rainfall, but precipitation was generally consistent. One exception was the 3 inches of rain in mid-July which resulted in some flooding in one of the replications. Two to three inches of rain occurred in late August at the end of the study. A total of 24 inches of rain occurred at the field planting site in Clinton, NC throughout the duration of the study.

Study Design and Data Collection

The study used a randomized complete block design with 4 replications. There was a total of 5 harvests collected over 34 days (21 July through 24 August) with some harvests spanning 2-4 days. Fruits were picked when signs indicated they were ripe; yellow to tan ground spot, dead tendrils, ribbing, color. Fruits were counted and weighed individually. Fruit with pest damage and or rot were weighed and counted if the fruit was intact and representative of the rest of the plot. Vines were moved to cover unpicked fruit that were exposed during the harvests.

Quality Evaluations

Measurements were taken on 20 fruit (5 per block) of each cultigen to determine the fruit size, fruit shape, soluble solids (sweetness of Brix), interior flesh firmness, flesh color, rind thickness, seed trace size, hard seed population, and hollowheart. The most representative fruit were selected for quality measurements and measurements were retaken on another fruit if necessary. Soluble solids were measured by cutting a piece of flesh from the center of the fruit and squeezing out the fruit juice onto the digital refractometer (Atago, Vernon Hills, IL). Flesh firmness was taken using a Penetrometer FT 011 with a 7/16’ plunger tip (QA Supplies LLC, Norfolk, VA), and was recorded in pounds. Samples were obtained by cutting the center of the fruit from the stem to blossom end. Pressure was then taken in five areas of the fruit: stem end, top side, ground spot side, blossom end, and center. The reported measures on flesh firmness are an average of the five sample areas; pressure was not taken on fruit with hollowheart. Hard seed in triploid fruit was determined according to the USDA standards. Fruits were cut longitudinally in half, and then the halves were cut laterally. The number of hard seeds exposed on the cut surface were counted and recorded. Most of the quality measurements were taken in the early harvests (1-2). Additional information on the quality measurements is presented in the Quality section on page 12 and in Table 8.

Financial Support

In addition to seed companies, this research was supported by the College of Life and Agricultural Sciences, North Carolina Agriculture Research, the North Carolina Cooperative Extension Services, and the North Carolina Department of Agriculture and Consumer Services. This work was in part supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2020-51181-32139 (CucCap).

Results and Discussion

Overall fruit yield and quality were good for the duration of the study. Heavy rains and a low area in the field resulted in flooding in some plots in the third rep. Plots affected were removed from the analysis to provide the best representation of the cultigen’s yield and quality response. For the analysis, fruits were placed in the following categories: < 9 lb, 9-13.4 lb, 13.5-17.4 lb, 17.5-21.4 lb, and ³ 21.5 lb. The diploid (seeded) cultigen Estrella from Syngenta, the yellow flesh cultigen Buttercup from Seedway, and popular cultigen Fascination from Syngenta were included as comparison. Cracker Jack from Enza Zaden is a cultigen gaining popularity in North Carolina and more recently used as a comparison cultigen.

Cumulative Harvests (1-5)

Yield: Pounds per acre

The orange flesh cultigen Orange Crisp (Figure 2) from US Seedless had the highest marketable yield of all 33 entries in this study at 89,577 pounds per acre (Mkt lb/ac) (Table 4). Marketable fruit do not include fruit that fall into the less than 9-pound category (< 9lb). Guardsman from Seedway, a red flesh cultigen, had the seond highest marketable yield at 87,027 lb/ac. The average marketable yield across all 33 entries was 59,845 lb/ac. Popular cultigens Fascination and Cracker Jack had marketable yields of 76,050 and 56,674 lb/ac, and were ranked sixth and eighteenth, respectively. The majority of the yield in this study fell into the 9-13.4 and 13.5-17.4 lb categories. ‘Orange Crisp’ and ‘Guardsman’ differed statistically in marketable yield with ‘53022’, ‘Marshall’, ‘Orchid Sweet’, and ‘Amarela’ (Table 4).

Yield: Number of fruit per acre and number of fruit per plant

‘Orange Crisp’ from US Seedless had the highest number of marketable fruit per acre (Mkt no/ac) at 5518 (Table 5). ‘Guardsman’ from Seedway had the second highest number of marketable fruit per acre at 5169. The average number of fruit per acre across all entries was 4050. ‘Cracker Jack’ and ‘Fascination’ had 3833 and 3775 fruit per acre, and were ranked eighteenth and twentieth, respectively. ‘Nun 32126’ (Figure 3) from BASF/Nunhems had the highest number of fruit per plant (Fruit no/plant) at 3.7. Most of the fruit harvested in this study were in the 9-13.0 lb category.

Yield: Bins per acre

‘Orange Crisp’, the orange flesh entry from US Seedless, had the highest number of bins with marketable fruit per acre (Mkt bins/ac) across all entries with 128 bins (Table 6). Marketable bins does not include fruit in the less than 9-pound category (< 9lb). ‘Guardsman’ from Seedway had the second highest number of bins at 124. The average number of bins per acre across all cultigens was 85. Cultigens Fascination and Cracker Jack had 109 and 81 bins with marketable fruit per acre and were ranked sixth and eighteenth, respectively. The majority of bins were of fruit in the 9-13.4 and 13.5-17.4 lb categories.

Yield: Average fruit size and bin size distribution

The diploid (seeded) cultigen Estrella from Syngenta produced the largest fruit in the study with an average of 18.1 pounds per fruit (Table 7). ‘Guardsman’ (Figure 4) produced the second largest fruit with an average weight of 16.3 pounds per fruit. ‘Guardsman’ had 54% of its fruit in the 30 and 36-count bin categories. The average fruit weight across all 33 entries was 13.8 pounds with a range from 18.1 to 9.9 pounds per fruit. Cultigens Fascination and Cracker Jack had average fruit weights of 14.9 and 14.0 pounds per fruit, and were ranked eighth and seventeenth, respectively.

‘Estrella’ also had the largest percentage of fruit in the 30-count bin category at 38% followed by ‘Guardsman’ at 31%. ‘Virtue’ from Syngenta and ‘Essence’ from Origene had the highest percentage of fruit in the 36-count bin category at 32% for both entries. ‘3F93-2487’ from Known You Seed and ‘Rio Grande’ from Enza Zaden had the highest percentage of fruit in the 45-count bin category at 43%.

Quality:

‘HMC633800’ from HM Clause was the sweetest of all 33 entries with an average Brix of 12.5 (Table 8). Brix is a measure of sweetness, and the units equate to 1 gram of sucrose in 100 grams of solution. All four of HM Clause’s entries were the top cultigens for sugar content in this study; HMC633800, Eleanor, HMC633248, and HMC633239. The average sugar content across all 33 entries was 11.6 with the majority of fruit having a rating above 11.0.

The two entries with the firmest flesh were ‘Cato (WDL9432)’ (Figure 5) from Syngenta and ‘Sweet Trick’ from Bayer/Seminis with an average firmness of 5.0 and 4.8 pounds, respectively (Table 8). These two cultigens were also the lowest for sweetness.

‘Cato (WDL9432)’ and ‘Virtue’ from Syngenta had the highest color ratings out of all entries with an average color rating of 4.9 for both entries; color is based on a 1 to 5 scale with 1 being pale or white and 5 being a deep blood red (Table 8). Flesh color was good in this study, with an average color rating of 4.5.

‘Sweet Trick’ from Bayer/Seminis had the thinnest rind at 14.4 mm (Table 8). The cultigen with the thickest rind was Warrior from BASF/Nunhems at 19.9 mm. The average rind thickness across all cultigens was 16.3 mm.

The cultigens Essence from Origene, 3F93-2487 from Known You Seed, and Buttercup from Seedway had the lowest population of hard seeds with an average of 0.2 hard seeds per fruit (Table 8). ‘WDL9454’ from Syngenta had the highest population of hard seeds at 6.8 seeds per fruit, the average across all cultigens was 2.0 hard seeds per fruit.

‘Eleanor (HMC633802)’ from HM Clause had smallest seed trace in the study at a rating of 0.7; seed trace was measured on a 1-5 scale with 1 being small and 5 being large (Table 8). Overall, seed trace size was small across all entries with an average rating of 1.3.

Quality: Hollowheart

Nearly half of the cultigens in this study had no incidence of hollowheart (Table 9). Of those that did have hollowheart, only 6 cultigens had any fruit with a rating of 3 or higher; a rating of 3 or 4 are considered unmarketable.

Early Harvests (1-2): 21 and 24 July (harvest 1); 28 July and 1 August (harvest 2)

Early Yield: Pounds per acre

The orange flesh cultigen Orange Crisp from US Seedless had the highest marketable yield in the early harvests with 54,113 pounds per acre (lb/ac) (Table 10). ‘Fascination’ was ranked third with 40,017 lb/ac. The average marketable yield for the early harvests was 28,469 lb/ac. The majority of the yield in the early harvest fell into the 13.5-17.4 pound category. ‘Orange Crisp’ differed statistically in marketable yield in the early harvests with ‘Cato (WDL9432)’ and with the 17 entries that followed it in Table 10.

Early Yield: Number of fruit per acre and number of fruit per plant

‘Orange Crisp’ had the highest number of marketable fruit per acre (Mkt no/ac) at 3136 and also had the highest number of fruit per plant (Fruit no/plant) at 1.9 for the early harvests (Table 11). ‘HMC633239’ from HM Clause ranked second for highest number of marketable fruit per acre and was the leader among the red-fleshed cultigens with 2439 fruit per acre. The average number of marketable fruit across all entries was 1797 fruit per acre and the average number of fruit per plant was 1.1

Early Yield: Bins per acre

‘Orange Crisp’ from US Seedless and ‘Estrella’, ‘Fascination’, and ‘Virtue’ from Syngenta had the highest number of bins with marketable fruit per acre for the early harvests at 77, 62, 57, and 57 bins/ac, respectively (Table 12). The average number of bins with marketable fruit per acre in the early harvests was 41. Most of the fruit fell into the 13.5-17.4 lb category.

Early Yield: Average fruit size and bin size distribution

‘Guardsman’ from Seedway had the second largest fruit on average at 19.4 lb/fruit for the early harvest (Table 13). ‘Estrella’, a seeded cultigen from Syngenta, had the highest average fruit weight at 20.6 pounds per fruit. ‘Guardsman’ was a pound heavier than the next largest cultigen Essence (Figure 6) from Origene which was 18.4 lb/fruit. ‘HMC633239’ from HM Clause ranked eleventh for average fruit weight at 15.9 lb/fruit. This cultigen had the highest number of marketable fruit per acre but ranked fifth for marketable pounds per acre for the early harvests which is explained by its smaller fruit size. The average fruit size across all cultigens was 15.2 lb/fruit.

‘Estrella’ and ‘Guardsman’ both had nearly 50% of their fruit fall into the 30-count bin category in the early harvests at 48% and 47%, respectively (Table 13). ‘Essence’ from Origene had the highest percentage of fruit in the 36-count bin category at 46%. Most of the fruit in the early harvests were in the 45-count bin category with an average of 36% of bins falling into that category.

Mid-Season Harvests (3-4): 8 and 10 August (harvest 3) and 15 August (harvest 4)

Mid-Season Yield: Pounds per acre

The cultigen Guardsman from Seedway had the highest marketable yield at 47,091 pounds per acre (Mkt lb/ac) for the mid-season harvests (Table 14). The average marketable yield was 24,378 lb/ac. Most of the yield for the mid-season harvests fell into the 9-13.5 lb category. ‘Guardsman’ differed statistically in marketable yield with ‘7197HQ’ and with 9 other entries with less yields (Table 14).

Mid-Season Yield: Number of fruit per acre and number of fruit per plant

‘Buttercup’, a yellow flesh cultigen from Seedway, had the highest number of marketable fruit per acre (Mkt no/ac) for the mid-season harvests at 2904 (Table 15). ‘Guardsman’ from Seedway and ‘Sweet Trick’ from Bayer/Seminis were ranked second and third for the highest number of marketable fruit per acre at 2846, and 2556, respectively. The average number of marketable fruit across all entries was 1698 no/ac. ‘Buttercup’ also had the highest number of fruit per plant (Fruit no/plant) for the mid-season harvests at 2.0. The average number of fruit per plant was 1.2 for harvests 3 and 4.

Mid-Season Yield: Bins per acre

‘Guardsman’ from Seedway had the highest number of bins with marketable fruit per acre (Mkt bins/ac) with 67 for the mid-season harvests followed by ‘Miramonte (XWT9161)’ from Sakata and ‘Sweet Trick’ from Bayer/Seminis with 61 and 53 bins with marketable fruit per acre, respectively (Table 16). The average number of bins was 35 for the mid-season harvests. Most bins contained fruit in the 9-13.4 lb category.

Mid-Season Yield: Average fruit size and bin size distribution

‘Miramonte (XWT9161)’ (Figure 7) from Sakata, ‘Guardsman’ from Seedway, and ‘Estrella’, the diploid (seeded) cultigen from Syngenta, had the largest fruit for the mid-season harvests at 16.5, 15.7, and 15.5 lb/fruit, respectively (Table 17). The average fruit weight across all 33 entries was 13.2 lb/fruit.

‘Miramonte (WXT9161)’ had the highest percentage of fruit in the 30-count bin category for the mid-season harvests with 37%. ‘Estrella’ had the highest percentage of fruit in the 36-count bin category at 35% followed by ‘Eleanor (HMC633802)’ from HM Clause with 33%. ‘HMC633248’ from HM Clause had the highest percentage of fruit in the 45-count bin category at 46%. The majority of cultigens had fruit in the 60-count bin category with 36% of the distribution falling into that category.

Late Harvest (5): 24 August

Late Yield: Pounds per acre

‘Virtue’ from Syngenta, ‘Miramonte (XWT9161)’ from Sakata, and ‘Nun 32126’ from BASF/Nunhems had the highest marketable yields for the late harvest with 14956, 14793, and 14,334 lb/ac, respectively (Table 18). The average marketable yield for the late harvest across all 33 entries was 6998 lb/ac. Fruit were generally smaller in the late harvest with only seven cultigens having fruit in the 17.5-21.4 lb category and only three cultigens having fruit greater than or equal to 21.5 lb. The were no statistical differences in marketable yield for the late harvest, as yields across replications varied considerably due to vine health.

Late Yield: Number of fruit per acre and number of fruit per plant

‘Nun 32126’ from BASF/Nunhems had the highest number of marketable fruit per acre (Mkt no/ac) for the late harvest at 1278 (Table 19). There was less fruit overall in the late harvest compared to the early and mid-season with an average of 554 marketable fruit per acre. ‘Nun 32126’ from BASF/Nunhems and ‘Miramonte (XWT9161)’ from Sakata were the only two entries that had over 1000 marketable fruit per acre; the other entries ranged from 987 to 116. ‘Nun 32126’ was the only entry to have 1.0 or more fruit per plant. The average fruit per plant across all entries was 0.2. Vine health declined substantially since the fourth harvest.

Late Yield: Bins per acre

‘Miramonte (XWT9161)’ from Sakata and ‘Virtue’ from Syngenta had the highest number of bins with marketable fruit per acre (Mkt bins/ac) for the late harvest at 21 bins/ac (Table 20). The average number of bins per acre was 10 across all entries. Most entries did not have fruit in the 17.5 to 21.4 lb category and only three entries had fruit in the greater than or equal to 21.5 lb category.

Late Yield: Average fruit size and bin size distribution

‘Warrior’ from BASF/Nunhems had the highest average fruit weight for the late harvest at 14.2 lb/fruit which was nearly a pound heavier than the next largest entries ‘Essence’ from Origene and ‘HMC633800’ from HM Clause at 13.3 lb/fruit (Table 21). The average fruit weight across all 33 entries was 11.5 lb for the late harvest with a range from 14.2 lb to 8.3 lb. Only three entries had fruit in the 30-count bin category and only seven had fruit in the 36-count bin category. Most fruit for the late harvest were in the 60-count bin category, which had an average of 46% of the fruit across all entries.