Hort. Series # 248

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.

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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 2024 cultigen evaluation study. We want to acknowledge summer employees Lia Hunt, Daphne Meyer, Cameron Roberts, and Nathaniel Wyshka for their assistance with this study. The cooperation and support of BASF/Nunhems, Hazera, Known You Seed, Rijk Zwaan, Seminis, Syngenta, and U.S. Agriseeds 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 mini size triploid watermelon cultigen evaluation study conducted during 2024. 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.

Financial Support

In addition to seed companies, this research was supported by the College of Life and Agricultural Sciences, North Carolina Agriculture Research and 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).

Introduction

In 2022-2023, approximately 320 million pounds of mini watermelon were sold in retail markets in the U.S. In 2023-2024, about 328 million pounds of mini watermelon were sold, demonstrating a 1.9% increase from the previous year. In 2023-2024, mini watermelon accounted for 9.3% of watermelon sales in the U.S. The national average price of watermelon per pound increased by $0.02 as well, from $0.78 in 2022-2023 to $0.80 in 2023-2024.

In 2022-2023, approximately 38 million pounds of mini watermelon were sold in retail markets in the Southeast. This increased by 20.4% in 2023-2024, with approximately 46 million pounds sold. In 2023-2024, mini watermelon accounted for 9.2% of all watermelon grown in the Southeast.

Retail scanner data shows an increasing demand for mini watermelon in the California, Midsouth, Plains, Southcentral, and Southeast regions of the US, by 1.0%, 10.4%, 1.5%, 6.7%, and 20.4% respectively (watermelon.org). In North Carolina, demand for mini watermelon increased by 25.7% in the Charlotte area and by 17.8% in the Raleigh/Greensboro area.

In 2024, Dr. Schultheis and the Cultural Management Program in the Horticultural Sciences Department at NC State University conducted an evaluation of 15 mini size triploid (seedless) watermelon cultigens from 7 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 are presented below (Figures 2-16).

Materials and Methods

Sowing and Field Preparations

Once all seeds were received from participating companies, they were planted into 72-cell poly trays (Hummert Int; Earth City, MO) to grow transplants. The mini watermelon cultigens were sown on 25 March 2024. 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. Transplants were fertilized once per 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 mini watermelons were planted in block E2; an Orangeburg loamy sand soil type. NPK fertilizer (10-10-10) at 500 lb/ac was applied on 1 April 2024. Pic 60 (6 gal/ac) fumigant was shank applied in-row with the bed shaper on 9 April 2024 for weed and nematode control. Black polyethylene plastic (1.25 mil thick, high density plastic film, 54 inches wide; TriEast Ag Group, Inc., Clinton, NC) was laid on 9 April 2024.

Transplanting and Vine Training

The mini triploid watermelon transplants were established in the field on 1 May 2024. Plot size for mini triploid watermelons was 1 row, 10 plants per row, 15 feet long with alleys of 10 feet between plots. Row middles were 10 feet and in-row spacing was 1.5 feet. Plots with missing plants were replaced 1 week after planting 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 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, and 50 units/ac K were all 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 the drip tape fertigation 19 times at rates of 15, 20, 25, or 35 gal/ac. Cumulative totals, preplant and through the drip tape, of applied fertilizer nutrients were: 166 units N, 50 units P, 314 units K, 33 units of S, and 16.5 units of Mg.

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

Weather

Weather was not consistent during the growing season, as both drought and flooding occurred across North Carolina. A period of drought occurred in June, during which the field site received less than 1 inch of rain in 30 days. A tropical storm system then brought heavy rain in late July, resulting in flooding of plots and rotting of fruit on the vine and ultimately leading to only harvesting the study three times, compared to seven harvests in 2023. A total of 17.5 inches of rain occurred at the field planting site in Clinton, NC throughout the duration of the study with the majority of the precipitation occurring over the last 2 weeks in July (Figure 1).

Study Design and Data Collection

The study used a randomized complete block design with 4 replications. There were a total of 4 harvests collected over 31 days (July 2 through 1 August). 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 12 fruit (3 per replication) of each cultigen to determine the fruit size, fruit shape, soluble solids (sweetness or 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 additional fruit if necessary. Soluble solids were measured by cutting a piece of flesh from the center of the fruit and squeezing the fruit juice onto a digital refractometer (Atago, Vernon Hills, IL). Flesh firmness was taken using a Penetrometer FT 011 with a 7/16” plunder 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 harvest (1). Additional information on the quality measurements is presented in the Quality section on page 8 and in Table 7.

Results and Discussion

A period of drought in the early season followed by heavy rains in July resulted in lower yields and fewer harvests in this year’s study.

For the analysis, fruits were placed in the following size categories: < 3 lb, 3 – 7 lb, 7.1 – 9 lb, and ≥ 9.1 lb.

Cumulative Harvests (1-3)

Yield: Pounds per acre

‘Romalinda’ from Seminis had the highest marketable yield out of all 15 entries in this study at 34,572 pounds per acre (lb/ac) (Table 4). ‘Amazing’ from Known You Seed ranked second with a marketable yield of 34,565 lb/ac, and ‘Expert’ from Hazera ranked third with a marketable yield of 31,407 lb/ac. The average marketable yield across all entries was 29,213 lb/ac. ‘Romalinda’ from Seminis, ‘Extazy’ from Hazera, and ‘Altata’ from Rijk Zwaan all produced over 16,000 lbs of oversized fruit (≥ 9.1 lb) that were not considered marketable as mini watermelons, otherwise these cultigens would have been ranked higher.

Yield: Number per acre and number of fruit per plant

The cultigen Amazing from Known You Seed had the highest number of marketable fruit per acre (Mkt no/ac) at 6,244 (Table 5). ‘Expert’ from Hazera ranked second at 5,445; ‘Petite Perfection’ from Syngenta, ‘Sugar Rush’ from US Agriseeds, and ‘3F-4109’ from Known You Seed all ranked third at 5,300. The average number of marketable fruit per acre across all 15 cultigens was 4,942.

‘Amazing’ from Known You Seed and ‘Romalinda’ from Seminis both had the highest number of fruit per plant at 2.4 (Table 5). However, ‘Romalinda’ only ranked eighth for marketable number per acre due to a large percentage of fruit being oversized and therefore not marketable. The larger fruits might be marketable but would fit the icebox size designation. Fruit number per plant ranged from a low of 1.7 to a high of 2.4. The average number of fruit per plant across all entries was 2.

Yield: Average Fruit Size and Distribution

‘Romalinda’ from Seminis had the largest fruit, on average, at 8.1 lb/fruit (Table 6). ‘Altata’ from Rijk Zwaan and ‘Extazy’ from Hazera both ranked second for average fruit size at 8 lb/fruit. The average fruit size across all 15 entries was 6.4 lb/fruit. ‘Crimson Belle’ and ‘Queenlet’ from Known You Seed, ‘Exceed’ from Hazera, and ‘Bolita’ from BASF/Nunhems were all above the average for fruit size.

Some cultigens had fruit that were unmarketable as mini size watermelons as they were greater than 9.1 lbs. 31% of ‘Extazy’, 30% of ‘Romalinda’, and 27% of ‘Altata’ fruit were in the greater than 9.1 lb (> 9.1 lb) size category. On average, across all 15 cultigens, 13% of fruit were oversized and therefore unmarketable as mini watermelons. Most fruit were in the 3-7 lb size category.

Quality

‘3F-4109’ from Known You Seed had the highest Brix or sugar content across all 15 cultigens at 12.0, followed by ‘Petite Perfection’ from Syngenta at 11.8 (Table 7). Brix is a measure of sweetness, and the units equate to 1 gram of sucrose in 100 grams of solution. The average sugar content across all entries was 11.3. ‘Amazing’, ‘Gentility’, ‘Crimson Belle’, and ‘Queenlet’ from Known You Seed, ‘Bolita’ and ‘Prelita’ from BASF/Nunhems, and ‘Romalinda’ from Seminis all had sugar contents above the average.

‘Extazy’ and ‘Exceed’ from Hazera had the two firmest flesh ratings across all 15 cultigens at 2.7 lb and 2.6 lb, respectively (Table 7). The average firmness of all entries was 1.8 lb.

‘Extazy’ had the highest flesh color rating out of all 15 entries at 4.7; color is based on a 1 to 5 scale with 1 being pale or white and 5 being a deep blood red (Table 7). The average flesh color rating for all entries was 4.4.

‘Petite Perfection’, ‘Amazing’, and ‘3F-4109’ had the smallest rind thickness measurements on average across all entries at 6.3 mm, 8.5 mm, and 8.8 mm, respectively (Table 7). The average rind thickness across all 15 entries was 10.5 mm.

‘Crimson Belle’ and ‘Prelita’ had the lowest hard seed populations across all 15 entries at 0 and 0.1, respectively (Table 7). Hard seed population was low overall, with an average population of 0.6 across all 15 cultigens.

‘Bolita’ and ‘Prelita’ from BASF/Nunhems had the smallest seed traces across all entries at 1.3 for both; seed trace was measured on a 1-5 scale with 1 being small and 5 being large (Table 7). ‘Queenlet’ had the largest seed traces on average at 2.1. Overall, seed traces were small, with an average size of 1.6.

Quality: Hollowheart

Hollowheart incidence was low in this study, with 8 out of 15 entries having no hollowheart. The entry with the greatest incidence of hollowheart was ‘Crimson Belle’, with 50% of fruit having some degree of hollowheart. Only one entry had fruit with a hollowheart rating of 3 or higher, which is considered unmarketable: ‘Amazing’ with 8.3% HH3 (Table 8).

Early Harvest (1): 2 July

Early Yield: Pounds per acre

In the early harvest (1), ‘Bolita’ from BASF/Nunhems had the highest marketable yield at 16,317 lb/ac (Table 9). ‘Amazing’ from Known You Seed had the second highest marketable yield at 14,948 lb/ac, and ‘Romalinda’ from Seminis had the third highest marketable yield at 13,449 lb/ac. The average marketable yield for the early harvest across all 15 entries was 9,793 lb/ac. ‘Sugar Rush’ from US Agriseeds, ‘3F-4109’ and ‘Queenlet’ from Known You Seed, ‘Prelita’ from BASF/Nunhems, and ‘Petite Perfection’ from Syngenta all had marketable yields above the average for the early harvest.

Early Yield: Number per acre

In the early harvest (1), ‘Amazing’ from Known You Seed had the highest number of marketable fruit at 2,831 (Table 10). ‘Bolita’ from BASF/Nunhems and ‘Petite Perfection’ from Syngenta ranked second and third with 2,759 and 2,541, respectively. The average number of marketable fruit in the early harvest across all 15 entries was 1,723. ‘Sugar Rush’ from US Agriseeds, ‘3F-3109’ and ‘Queenlet’ from Known You Seed, ‘Romalinda’ from Seminis, and ‘Prelita’ from BASF/Nunhems all had greater numbers of marketable fruit in the early harvest than the average.

Mid-season Harvest (2): 15 July

Mid-season Yield: Pounds per acre

In the mid-season harvest (2), ‘Extazy’ from Hazera had the highest marketable yield per acre at 21,098 lb/ac (Table 11). ‘Expert’ from Hazera had the second highest marketable yield at 19,878 lb/ac, and ‘Crimson Belle’ from Known You Seed ranked third at 19,486 lb/ac. The average marketable yield for the mid-season harvest across all 15 entries was 15,230 lb/ac. ‘Excite’ and ‘Exceed’ from Hazera, ‘Altata’ from Rijk Zwaan, and ‘Sugar Rush’ from US Agriseeds all yielded above the average for the mid-season harvest.

Mid-season Yield: Number per acre

In the mid-season harvest (2), ‘Expert’ from Hazera had the highest number of marketable fruit per acre at 3,340 (Table 12). ‘Extazy’ from Hazera and ‘Crimson Belle’ from Known You Seed ranked second and third at 3,194 and 3,122 respectively. The average number of marketable fruit per acre in the mid-season harvest was 2,493. ‘Excite’ and ‘Exceed’ from Hazera, and ‘Gentility’ and ‘Amazing’ from Known You Seed all yielded greater than the average for the mid-season harvest.

Late Harvest (3): 23 July

Late Yield: Pounds per acre

In the late harvest (3), ‘Romalinda’ from Seminis had the highest marketable yield per acre at 7,598 lb/ac (Table 13). ‘Queenlet’ from Known You Seed had the second highest marketable yield at 7,489 lb/ac, and ‘Prelita’ from BASF/Nunhems had the third highest marketable yield at 5,082 lb/ac. The average marketable yield across all 15 cultigens for the late harvest was 4,190 lb/ac. ‘Gentility’, ‘Crimson Belle’, ‘Amazing’, and ‘3F-4109’ from Known You Seed all had marketable yields above the average for the late harvest.

Late Yield: Number per acre

In the late harvest (3), ‘Queenlet’ from Known You Seed had the highest number of marketable fruit at 1,234 (Table 14). ‘Romalinda’ from Seminis ranked second at 1,089, and ‘Expert’ from Hazera and ‘Gentility’ from Known You Seed both ranked third at 944. The average number of marketable fruit across all 15 cultigens for the late harvest was 726. ‘Amazing’ and ‘3F-4109’ from Known You Seed and ‘Prelita’ from BASF/Nunhems all yielded above the average for the late harvest.