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Hort Series #244

Principal Investigators: Jonathan R. Schultheis, Professor and Extension Specialist, Department of Horticultural Science, NC State University; Baker E. Stickley, Research Assistant, 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; 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, Hazera, Origene Seeds, Known You Seed, Rijk Zwaan, 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 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 2021-2022, approximately 305 million pounds of mini watermelon were sold in retail markets across the U.S. In 2022-2023, approximately 324 million pounds of mini watermelon were sold, making up 10.1% of total watermelon sales and demonstrating an increase of 6.4% from the previous year. The price per pound of mini watermelon increased by $0.02 as well, averaging $0.78 per pound in 2022-2023 versus $0.76 in 2021-2022.

Retail scanner data shows growing demand for mini watermelons in the Mid-South and Southeast regions of the US, which demonstrated 28.4% and 16.4% increases in mini watermelon sales, respectively. North Carolina is one of the top 5 watermelon producing states in the U.S and in 2022-2023 demand for mini watermelon increased by as much as 49.3% in the Raleigh/Greensboro area and 46.7% in the Charlotte area (watermelon.org) compared to 2021-2022.

In 2023, Dr. Schultheis and the Cultural Management Program in the Horticultural Sciences Department at NC State University conducted an evaluation of 16 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 2-17).

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 28 and 29 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 planting. Transplants were fertilized 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 mini watermelons were planted in block 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 mini triploid watermelon transplants were established in the field on 9 May 2023. 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 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 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 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 4). 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 7 harvest collected over 56 days (7 July through 1 September). 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 additional 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 8 and in Table 7.

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 resulted in flooding in some parts of the field and increased disease pressure in the standard size watermelon study, but the mini watermelon plots were largely unaffected. For the analysis, fruits were placed in the following categories: < 3 lb, 3 – 7 lb, 7.1 – 9 lb, and ≥ 9.1 lb.

Cumulative Harvests (1-7)

Yield: Pounds per acre

‘Sugar Rush’ from US Agriseeds had the highest marketable yield of all 16 entries in this study at 88,151 pounds per acre (lb/ac) (Table 4). ‘Excite’ from Hazera ranked second with a marketable yield of 80,499 lb/ac, and ‘Proxima’ from Origene ranked third with a marketable yield of 79,432 lb/ac. Average marketable yield across all entries was 69,959 lb/ac. Cultigens ‘Exceed’ and ‘Extazy’ from Hazera, ‘Petite Perfection’ from Syngenta, and ‘Bolita’ from BASF/Nunhems all yielded above the average. The majority of the yield in this study fell into the 3-7 lb category. ‘70475’ and ‘Altata’ had a substantial tonnage (40,387 and 37,895 lb/ac, respectively) that produced oversized fruits (> 9.1 lb) that were not considered marketable, otherwise, these cultigens would have ranked much higher.

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

The cultigen Sugar Rush from US Agriseeds had the highest number of marketable fruit per acre (Mkt no/ac) at 14,520 (Table 5). ‘Proxima’ from Origene ranked second with 13,576 no/ac, and ‘Petite Perfection’ from Syngenta ranked third at 13,141 no/ac. The average number of marketable fruit per acre across all 16 entries was 11,851. Cultigens Excite from Hazera, Amazing and Gentility from Known You Seed, and Bolita from BASF/Nunhems all yielded above the average.

‘Sugar Rush’ had the highest number of fruit per plant at 5.7 across all 16 entries. ‘Proxima’ ranked second for number of fruit per plant (Fruit no/plant) at 5.4. ‘Altata’ from Rijk Zwaan and ‘70475’ from Origene both ranked third for number of fruit per plant at 5.1 but ranked thirteenth and fourteenth for marketable number per acre, respectively, due to many fruit being greater than 9.1 lb and therefore unmarketable as a mini size watermelon. Fruit number per plant ranged from a low of 4.2 to a high of 5.7.

Yield: Average Fruit Size and Distribution

‘Exceed’ from Hazera had the largest fruit, on average, at 6.6 lb/fruit (Table 6). ‘70475’ from Origene and ‘Excite’ from Hazera ranked second and third for average fruit size at 6.4 lb/fruit and 6.3 lb/fruit, respectively. The average fruit size across all 16 cultigens was 5.9 lb/fruit. ‘Extazy’ from Hazera, ‘Altata’ from Rijk Zwaan, ‘Melania’ from Origene, ‘Queenlet’ from Known You Seed, and ‘Sugar Rush’ from US Agriseeds all were above the average for fruit size.

Some cultigens had fruit that were considered unmarketable as mini size watermelons as they were greater than 9.1 lb. 25% of ‘70475’, 22% of ‘Altata’, and 19% of ‘Queenlet’ fruit harvested were in the greater than 9.1 lb (> 9.1 lb) size category. On average, across all 16 cultigens, 10% of fruit were oversized and therefore unmarketable as mini size watermelons. Most fruit were in the 3-7 lb category.

Quality

‘Exceed’ from Hazera had the highest Brix or sugar content across all 16 cultigens at 11.7, followed by ‘Petite Perfection’ from Syngenta at 11.6 (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 11.0. ‘Amazing’, ‘3F-4109’, and ‘Crimson Belle’ from Known You Seed and ‘Melania’ from Origene all had above average sugar content at 11.2 and 11.1.

‘Onza’ from Hazera and ‘70475’ from Origene had the two firmest flesh ratings across all 16 entries at 4.3 lb and 3.8 lb, respectively (Table 7). The average firmness of all entries was 3.2 lb.

‘Exceed’ had the highest flesh color rating out of all 16 entries at 4.8; 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’, ‘Gentility’, and ‘Amazing’ had the smallest rind thickness measurements on average across all entries at 8.3 mm, 8.6 mm, and 9.8 mm, respectively (Table 7). The average rind thickness across all 16 entries was 12.7 mm.

‘Amazing’ and ‘Bolita’ had the lowest hard seed population across all 16 entries at 0.1 for both entries (Table 7). Hard seed population was low overall, with an average population of 0.7 across all 16 cultigens.

‘Onza’ had the smallest seed traces across all entries at 0.8; seed trace was measured on a 1-5 scale with 1 being small and 5 being large (Table 7). ‘Queenlet’ and ‘Gentility’ had the largest seed traces on average at 1.8 for both entries. Overall, seed traces were small, with an average size of 1.3.

Quality: Hollowheart

Hollowheart incidence was low in this study, with 10 out of 16 entries having no hollowheart. The entry with the greatest incidence of hollowheart was ‘Queenlet’, with 45% of fruit having some degree of hollowheart. Three entries had fruits with a hollowheart rating of 3 or higher, which are considered unmarketable: ‘Crimson Belle’ with 5% HH3 and 5% HH4, ‘Amazing’ with 20% HH3, and ‘Queenlet’ with 15% HH3 and 5% HH4 (Table 8).

Early Harvests (1-2): 7 July (harvest 1) and 18 July (harvest 2)

Early Yield: Pounds per acre

In the early harvests (1-2), ‘Queenlet’ from Known You Seed had the highest marketable yield at 19,471 lb/ac (Table 9). ‘Bolita’ from BASF/Nunhems had the second highest marketable yield at 16,688 lb/ac, and ‘Altata’ from Rijk Zwaan had the third highest at 16,543 lb/ac. The average marketable yield across all 16 entries for the early harvests was 14,100 lb/ac. ‘Petite Perfection’ from Syngenta, ‘Excite’ from Hazera, and ‘Crimson Belle’ from Known You Seed all yielded above the average for the early harvests.

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

In the early harvests (1-2), ‘Petite Perfection’ from Syngenta and ‘Queenlet’ from Known You Seed had the highest marketable number of fruit at 3,122 no/ac for both entries (Table 10). ‘Amazing’ from Known You and ‘Bolita’ from BASF/Nunhems ranked second and third with 3,001 no/ac and 2,710 no/ac, respectively. The average number of marketable fruit across all 16 entries for the early harvests was 2,423 no/ac. ‘Gentility’, ‘Crimson Belle’ and ‘3F-4109’ from Known You Seed, ‘Altata’ from Rijk Zwaan, and ‘Onza’ from Hazera all yielded more marketable fruit than the average for the early harvests.

‘Queenlet’ had the highest number of fruit per plant at 1.3 no/plant, but many were unmarketable due to being greater than 9.1 lb. ‘Altata’ had the second highest number of fruit per plant at 1.2 no/plant but had similar issues with oversized fruit. ‘Petite Perfection’ and ‘Amazing’ both yielded 1.1 no/plant but had no oversized fruit and therefore increased marketable yield.

Mid-season Harvests (3-5): 26 July (harvest 3), 3 August (harvest 4) and 10 August (harvest 5)

Mid-season Yield: Pounds per acre

In the mid-season harvests (3-5), ‘Proxima’ from Origene had the highest marketable yield per acre at 39,153 lb/ac (Table 11). ‘Excite’ from Hazera and ‘Sugar Rush’ from US Agriseeds ranked second and third at 38,623 lb/ac and 37,890 lb/ac, respectively. The average marketable yield across all 16 entries for the mid-season harvests was 30,568 lb/ac. ‘3F-4109’ and ‘Gentility’ from Known You, ‘Petite Perfection’ from Syngenta, and ‘70475’ from Origene all yielded above average for the mid-season harvests.

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

In the mid-season harvests (3-5), ‘Proxima’ from Origene had the highest number of marketable fruit at 6,607 no/ac (Table 12). ‘Gentility’ from Known You Seed and ‘Sugar Rush’ from US Agriseeds both ranked second at 6,026 no/ac. The average number of marketable fruit for the mid-season harvests was 5,050 no/ac. ‘Excite’ and ‘Onza’ from Hazera, ‘3F-4109’ and ‘Crimson Belle’ from Known You Seed, and ‘Petite Perfection’ from Syngenta all yielded more marketable fruit than the average for the mid-season harvests.

‘Proxima’ from Origene also had the highest number of fruit per plant at 2.8 no/plant. ‘Excite’ from Hazera had the second highest number of fruit per plant at 2.6 no/plant but ranked fourth for marketable number per acre due to many fruit being oversized.

Late Harvests (6-7): 17 August (harvest 6) and 1 September (harvest 7)

Late Yield: Pounds per acre

In the late harvests (6-7), ‘Sugar Rush’ from US Agriseeds had the highest marketable yield per acre at 37,621 lb/ac (Table 13). ‘Exceed’ from Hazera and ‘Melania’ from Origene ranked second and third for marketable yield per acre at 33,570 lb/ac and 31,334 lb/ac, respectively. Both ‘Exceed’ and ‘Melania’ had over 12,000 lb/ac in oversized fruit, which is the primary reason that fruit were considered unmarketable. The average marketable yield across all 16 entries for the late harvests is 24,964 lb/ac. ‘Extazy’ and ‘Excite’ from Hazera, ‘Proxima’ from Origene, and ‘Petite Perfection’ from Syngenta all yielded above the average for the late harvests.

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

In the late harvests (6-7), ‘Sugar Rush’ from US Agriseeds had the greatest number of marketable fruit per acre at 6,389 no/ac (Table 14). ‘Melania’ from Origene and ‘Exceed’ from Hazera ranked second and third for marketable number per acre at 5,324 no/ac and 5,227 no/ac, respectively. The average number of marketable fruit per acre for the late harvests was 4,358 no/ac. ‘Proxima’ from Origene, ‘Extazy’ and ‘Excite’ from Hazera, and ‘Petite Perfection’ from Syngenta all yielded more marketable fruit per acre than the average in the late harvests.

‘Sugar Rush’ also had the greatest number of fruit per plant at 2.4 no/plant. ‘Exceed’ ranked second for number of fruit per plant at 2.3 no/plant but ranked third for marketable number per acre due to many oversized fruit in the late harvests.