Fruit set of seedless watermelons is reliant on growth hormones released by pollen tube growth and fertilization, the same as seeded watermelons. Pollen from the seedless plants, however, is not viable, thus it is crucial to have viable pollen from seeded cultivars transfer to the female flowers of the seedless plants. The plants that contribute pollen are called pollinizers or pollen donors. In general, the greater presence of male flowers from pollen donors within a given area will likely mean a greater probability of pollen transfer, and thus a greater yield of seedless watermelons. In addition, the timing and duration of male flower availability, plant growth pattern, and flower attractiveness to pollinators are also important characteristics of a pollenizer plant.
Growers may choose to use edible seeded cultivars as pollenizers, or specialized non-harvested pollenizers developed specifically for growing seedless watermelons. In some cases, growers may grow multiple pollenizer cultivars, or combine both traditional seeded cultivars and specialized pollenizers to ensure pollen is available throughout the flowering period of the seedless cultivar.
We used a pollenizer mixture this year in growing seedless watermelons. The pollenizer mixtures include ‘Premium’, ‘Accomplice’, ‘Ace Plus’, ‘Ace’, ‘SP7’, ‘800’ and ‘Wild Card Plus’. Meanwhile, we planted the pollenizers separately to compare their performance. ‘800’ and ‘Premium’ are edible seeded watermelons, the others are non-edible pollenizers. Here is a short summary of our observation (Figure 1).
‘Ace Plus’ had the most flowers in the first three weeks after transplanting; ‘Premium’ and ‘800’ had the least number of flowers in the first two weeks. At the fifth week, we found ‘SP7’ had the most flowers, followed by ‘Ace’, ‘Ace Plus’ and ‘Wild Card Plus’. ‘Accomplice’ and ‘Premium’ had fewer flowers, and ‘800’ had the least number of flowers. ‘Accomplice’ has a compact plant growth with short vines. ‘SP7’, ‘Ace’, ‘Ace Plus’ and ‘Wild Card Plus’ have long and thin vines and small foliage. ‘800’ had the densest canopies compared to the other pollenizer cultivars.
Figure 1. Pollenizer cultivar demonstration. Transplanted on May 16, 8′ apart between plants. Photos were taken on June 27.