TRIPLOID MINIWATERMELON CULTIGEN EVALUATION
SPRING 2004


D. N. Maynard and P. Perkins-Veazie
Gulf Coast Research and Education Center
University of Florida
5007 60th Street East
Bradenton, FL 34203

    Diploid (seeded) watermelons generally weigh from 18 to 35 lb and represent about 40% of the commercial crop grown in Florida. Triploid (seedless) watermelons usually weigh 15 to 22 lb and account for about 60% of the shipments from Florida. The proportion of the Florida crop devoted to triploid production is increasing each year. Icebox watermelons weigh 6 to 12 lb each and are grown on a very small acreage. Triploid personal size or miniwatermelons were introduced in 2003; these fruit weigh 3 to 8 lb. each. Production is expected to increase. Florida produced 7.2 million cwt of watermelons of all types from 24,000 harvested acres in 2003, which provided an average yield of 300 cwt/acre. The average price was $8.60/cwt resulting in a crop value of almost $62 million (Fla. Agr. Stat., 2004).

    Specialty vegetables are in high demand and seedless miniwatermelons offer an attractive alternative for discriminating consumers. Seedless miniwatermelons are being actively promoted by marketing organizations and seed companies to stimulate demand. At the same time, many new varieties are being developed and introduced.

The objective of this trial was to evaluate the performance of triploid miniwatermelon cultigens under west-central Florida conditions.

MATERIALS AND METHODS

    Seeds of 21 triploid miniwatermelon varieties or experimental hybrids from six different companies (Table 1) were planted in a peat-lite growing mix in planter flats (1 ¼ x 1 ¼ x 2 ¼ in. cells) on 2 February. The watermelon transplants were grown by a commercial plant grower.

    The EauGallie fine sand was prepared in mid February. Beds were formed and fumigated with methylbromide:chloropicrin, 67:33 at 350 lb/treated acre. Banded fertilizer was applied in shallow grooves on the bed shoulders after the beds were pressed and before the black polyethylene mulch was applied. The total fertilizer applied was equivalent to 150-40-208 lb N-P₂O₅-K₂O/A. The final beds were 32-in. wide and 8-in. high, and were spaced on 9-ft centers with four beds between seepage irrigation/drainage ditches, which were on 41-ft centers.
    The transplants were set in holes punched in the polyethylene mulch on 2 March at 1.5-ft in-row spacing that provided 13.5 ft²/plant. The replicated plots were 15 ft long and had ten plants each and were repeated three times in a randomized, complete block design. ‘SP-1' diploid watermelon transplants were interplanted every fourth plant to serve as the diploid pollenizer. Plant stands recorded just before vines grew together showed no significant differences among plots. Weed control in row middles was by cultivation and applications of paraquat. Pesticides were applied as needed for control of gummy stem blight (chlorothalonil, azoxystrobin, mancozeb, and maneb), and for lepidopterous larvae and silverleaf whitefly (Bacillus thuringiensis, endosulfan, bifenthrin, and spinosad).

    Watermelons were harvested on 24 May and 1 June. Marketable (U.S. No.1 or better) fruit according to U.S. Standards for Grades of Watermelons (U.S. Dept. Agr., 1978) were separated from culls and counted and weighed individually. Six fruit of each entry were sliced through the ground spot from stem to blossom end to obtain equatorial and polar dimensions. Using a metric caliper, rind thickness was measured in mm at four locations, starting at the blossom end and working in a counterclockwise direction. Firmness was measured at two locations within the fruit, just outside the heart, using a hand-held firmness gauge in 3 to 24 N (Wagner Force Dial, FDN 20, Greenwich, Ct.) with a 0.38 inch diameter flat probe. Average rind thickness and firmness measurements are presented in Table 4. A small sample (about 10 g) flesh was cut from the fruit heart and soluble solids content measured by squeezing juice onto a digital refractometer (Atago, Model PR 100). About 50 g tissue was sampled from the heart of each melon and placed in 50 ml polypropylene tubes. Tissue was frozen immediately using dry ice, shipped on dry ice to Lane, Okla. and held at -80 C until analyzed. Slightly thawed tissue was homogenized using a Polytron homogenizer (Brinkmann) to obtain a finely ground puree. The puree pH was measured using a pH meter (Orion Model 611) and electrode (Orion 8115). Absorbance of the puree at 560 and 700 mm was read using a Hunter Ultrascan XE colorimeter (Hunter Associates, Reston, VA), equipped with scanning diode array and xenon lights. To check colorimeter values, puree samples were also extracted with hexane:acetone:ethanol at a 2:1:1 ratio using the method of Fish et al. (2002), and absorbance at 503 mm determined by UV-vis spectrophometer (Shimazdu, UV-160). Lycopene solutions of known concentration were prepared with synthetic trans-lycopene (BASF) for calibration of the colorimeter and spectrophotometer. Where possible, data were subjected to analysis of variance and mean separation was by Duncan’s multiple range test.

RESULTS AND DISCUSSION

    Maximum temperatures were near average but minimum temperatures were below average throughout the growing period. This resulted in a later than usual crop. Rainfall was above average throughout the period, especially in April. Heavy winds caused some plant damage and restricted bee activity during the early flowering period.

    Yields of 3-8 lb miniwatermelons ranged from 5,807 fruit/acre for ‘Precious Petite’ to 14,196 fruit/acre for ‘Vanessa’ (Table 2). Nine other entries had fruit yields similar to those of ‘Vanessa’. Average fruit weight varied from 4.48 lb for ‘Precious Petite’ to 8.26 lb for YS03F01-0951/BLK. Fruit per plant ranged from 1.8 for ‘Precious Petite’ to 4.4 for ‘Vanessa’.

    The highest proportion of fruit in the 3 to 8 lb fruit weight class was 100% produced by ‘Precious Petite’; 99% of fruit of RWT 8154 and RWT 8155 and 98% of RWT 8162 fruit were in the 3 to 8 lb weight class (Table 3). On the other hand, over 40% of ‘Bobbie’, ‘Extazy’, HA 5109, ‘Mohican’, ‘Petite Treat’, ‘Valdoria’, and YS03F01-0951/BLK fruit exceeded 8 lb. The weight range of YS03F01-0951/BLK from smallest to largest fruit was 12 lb. The most uniform entries with respect to weight were ‘Petite Perfection’, ‘Precious Petite’, RWT 8154, RWT 8155, RWT 8162, and 3F-1824.

    Soluble solids ranged from 10.8% for YS01-331B to 15.5% for RWT 8154 (Table 4). Accordingly, all entries exceeded the 10% specified for optional use in the U.S. Standards for Grades of Watermelons to describe very good internal quality (U.S. Dept. Agr., 1928). Rind thickness (Table 4) varied from 0.2 inches for RWT 8154 to 0.7 inches for ‘Mohican’ and YS01-333B. Flesh firmness (Table 4) varied from 12.2 N for ‘Valdoria’ and ‘Vanessa’ to 23.0 N for Watermelon 5133; ‘Mohican’ flesh firmness was 22.2 N.

    The pH of melon purees exceeded 5.4, indicating melons were fully ripe when harvested. This is important as lycopene values are often 10-20% lower in unripe watermelons. Lycopene concentrations were highest (> 80 µg/g) in Hazera 6007, YS01-. 333B, ‘Mohican’, ‘Extazy’, ‘Precious Petite’, and YS01-331B (Table 4). However, fruit of all entries exceeded the 48.6 µg/g lycopene content given for watermelon in the USDA food composition database (USDA, 2004).

        Some desirable traits in miniwatermelon varieties are:

        * Production of high number of fruit per plant/acre;
        * Concentration of 3-8 lb fruit;
        * Oval or round shaped fruit;
        * Attractive striped or solid colored rind;
        * A thin, tough rind;
        * Deep red, crisp, sweet seedless flesh.

    ‘Vanessa’, HA 5109, ‘Petite Perfection’, ‘Bobbie’, RWT 8162, RWT 8155 and RWT 8149 produced more than 10,000 fruit per acre and more than 3 .0 fruit per plant. Of these entries ‘Petite Perfection’, RWT 8162, RWT 8155, and RWT 8149 produced at least 88% of their fruit in the 3-8 lb class. Thin rinds (0.3 inch) were found in ‘Petite Perfection’, RWT 8155, and RWT 8162. Accordingly, only three entries satisfy the traits measured in this trial: ‘Petite Perfection’, RWT 8155, and RWT 8162. Other entries will be commercially acceptable if less demanding criteria are used. Personally, I have only seen ‘Bambino’, ‘Mohican’ and ‘Petite Perfection’ in the supermarket where I shop.

    Triploid minimelons are an exciting new class of watermelons that are of special interest to one to two person households, households with children, and occasional watermelon consumers. It is likely that they will become a permanent segment of the watermelon market, but its size is difficult to estimate at this time.
 

 Note: The information contained in this report is a summary of experimental results. No discrimination is intended and no endorsement is implied where trade names are used.
 

ACKNOWLEDGMENT

    We are grateful to the following firms for their financial and material support of vegetable variety evaluation during 2002-2004. Abbott & Cobb; Agrisales, Inc.; BHN Research; Fafard Inc.; Harris Moran Seed Co.; Hazera Quality Seeds; Hollar Seeds; Nunhems (Sunseeds); Sakata Seed America; Shamrock Seed Co.; Seminis Vegetable Seeds, Inc.; Southwestern Vegetable Seed Co.; Sugar Creek Seeds, Inc.; Syngenta Seeds; U.S. Seedless, LLC; Willhite Seed, Inc.; and Zeraim Gedera Ltd.

LITERATURE CITED

Fish, W., P. Perkins-Veazie, and J.K. Collins. 2002. A quantitative assay for lycopene that utilizes reduced volumes of organic solvents. J. Food Comp. Anal. 15:309-317.

Florida Agricultural Statistics Service. 2004. Vegetables, acreage, production, value. Orlando, Fla.

U. S. Dept. Agr. 1978. U.S. standards for grades of watermelons. AMS, Washington, D.C.

U.S. Depat. Agr. Agr. Research Service. 2004. USDA National Nutrient Database for Standard Reference, Release 17. Nutrient Data Laboratory Home Page, http://www.nal.usda.gov/fnic/foodcomp

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