Effect of 2,4-D and CPPU on Triploid Watermelon Production and Quality

Pollination is one problem with intensive seedless watermelon ( Citrullus lanatus Thunb.) production under unfavorable environmental conditions (low solar radiation and temperature) due to the lowered activity of pollinating insects, such as the bee ( Apis mellifera L.). An alternative to overcome these problems is the use of plant growth regulators. For this reason, experiments were conducted for 2 years in plastic greenhouses in the fields of Almeria, southwestern Spain, to evaluate the production and quality of ‘Reina de corazones’ triploid watermelon grafted onto RS841 rootstock ( Cucurbita maxima × Cucurbita moschata ). Two phytoregulators were used for the development of the ovary: 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) and 2,4-dichlorophenoxyacetic acid (2,4-D). Concentrations of CPPU evaluated were 50, 100, 150, and 200 mg·L −1 . An application of 0.6 mL was applied to each ovary in addition to 4, 6, 8, or 12 mg·L −1 of 2,4-D to the foliar mass at a proportion of 1000 L·ha −1 . Results showed that the production and number of fruit obtained with CPPU treatments were similar to what is obtained by using bees for fruit pollination. Maximum production was reached at concentrations of 100–200 mg·L −1 . Average production was 32% to 83% higher than results from 2,4-D at 8 mg·L −1 . The number of fruit per plant was 33% to 35% higher as well. In the first assay, a positive correlation was also observed between production and CPPU concentration. CPPU treatments had a lower accumulation of sugars than those with 2,4-D; nevertheless, both treatments showed values of commercially acceptable soluble solids.