Fruit Yield and Quality of Heirloom Watermelon Cultivars Grown Organically

Watermelon is a popular fruit vegetable due to its delicious flavor and for being a source of vitamins and antioxidants. Majority of watermelon cultivars used commercially are triploid hybrids that produce seedless fruit. Triploid hybrids were produced by mutations and are not presently acceptable for organic production. There is currently scant information on organic production of watermelon in the southeast U.S.  The objective was to evaluate the yield of organic watermelon heirloom cultivars.  Experiment was conducted in Tifton, GA, in spring of 2015 in organically certified land.  Soil is loamy sand, with a pH of about 6.5. Watermelon was planted on 6 May 2015 on raised beds (1.8-m centers) with drip tape and black plastic mulch. Prior to making the bed, 5529 kg/ha of organic fertilizer (microSTART 3-2-3, Perdue AgriRecycle, LLC) was applied. Cultivars evaluated were: Moon & Stars (Cherokee), Sweet Siberian OG, Mtn. Sweet Yellow, Moon & Stars (VDoren), Petite Yellow, Chris Cross, Chelsea, Moon & Stars (Yellow), Golden Midget, Cream Saskatchewan, and Picnic. Fruit were harvested from 18 June to 14 July 2015. Individual fruit were graded and weighed according to USDA grading standards. Fruit soluble solids (SSC) (measured with a refractometer) and titratable acidity (TA) were determined. Mean seasonal air temperature was 23.5 °C; cumulative rainfall was 114 mm.  Marketable yield was highest in ‘Chris Cross’ (58.1 t/ha) and lowest in Petite Yellow (32.0 t/ha). Fruit weight was lowest in ‘Golden Midget’ (2.1 kg) and highest in ‘Chelsea’ (7.3 kg). Soluble solids were highest in ‘Chelsea’ (7.96%) and ‘Mountain Sweet Yellow’ (7.88%) and lowest in ‘Golden Midget’ (4.99%). Titratable acidity was highest in ‘Cream Saskatchewan (0.518%) and lowest in ‘Moon & Stars’ (Cherokee) (0.389%) and ‘Golden Midget (0.380%). SSC/TA ratio was greatest in ‘Moon & Stars’ (Cherokee) (19.9%). Across cultivars, values of SSC were low and those of TA were high likely because fruit were harvested before reaching ripe stage. However, increased incidence of fruit decay was observed in ripe fruit or as fruit approached the ripe stage. Thus, determination of proper harvest index for heirloom watermelon cultivars is important to maximize fruit quality and reduce postharvest losses.