Investigation of management strategies to improve fruit set in seedless watermelon (Citrullus lanatus var. Lanatus)
Date
2017
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Publisher
University of Delaware
Abstract
Watermelon (Citrullus lanatus) is an economically important crop in the Delaware-Maryland region with over 5000 acres grown annually. Seedless watermelons account for over 80% of the acreage in Delaware, and diploid pollenizers are necessary to provide pollen for triploid seedless watermelon development. However, due to spring weather variability on the Delmarva Peninsula, growers often face challenges with early fruit set. Reasons for this include limited bee activity in cold, rainy weather conditions and poor transplant vigor under these conditions. ☐ The goal of this research was to explore areas that could improve early and overall fruit set. These included examining flower timing and pollen viability of pollenizer cultivars, identifying the effects of application of plant growth regulators during crown set, and determining what links there might be between pollenizer and seedless cultivars when planted alongside one another. All research was conducted during the summers of 2014 and 2015 at the University of Delaware’s Carvel Research and Education Center, Thurmond Adams Agricultural Research Farm located in Georgetown, Delaware. ☐ Staminate flowers were counted and collected from 24 different pollenizers with two different planting dates per year. Pollen was removed from those flowers and stained to determine viability. Pollen was then stained using acetocarmine solution and counted under the microscope. Male flower counts were found to range from a low of 2.8 flowers in May to a high of 11.4 in June, showing a wide range of pollen availability. Furthermore, pollen viability ranged from 76.12 to 81.04%, a difference of less than 5% between the pollenizer with the highest pollen viability and the lowest. This is valuable information for pollenizer selection by growers. ☐ Plant growth regulator applications showed significant differences from the untreated controls in 2014 but not in 2015. Watermelons treated with Promalin had the highest yields in 2014 at 85184.65 Kg/Ha, and Radiate treated watermelons had the highest yields in 2015 at 45095.44 Kg/Ha. The Promalin watermelons in 2014 were significantly different than the untreated control, but the 2015 Radiate watermelons were not (P = 0.05). Weather conditions likely played a major role in these differences. More testing must be done on these compounds before effort should be made to get these products on-label for watermelon production in Delaware and Maryland. ☐ Finally, certain pollenizers performed well across multiple cultivars of seedless watermelon. ‘Pollen Pro’ and ‘Premium’ are two modern pollenizer cultivars that could be recommended to area growers no matter which cultivar of seedless watermelon they wished to grow. ‘Pollen Pro’, when used as a pollenizer for cultivar 7187 in 2015, produced almost twice as many fruit as the lowest producing pollenizer (6100 vs. 3200). Furthermore, cv. 7187 plants planted alongside ‘Pollen Pro’ had the highest yields for that seedless cultivar. When used as a pollenizer, the cultivar ‘Premium’ produced yields that were in the upper half of all three seedless cultivars, even if these differences were not statistically significant (P = 0.05). However, this research would have benefited greatly from one more year of data collection due to the great differences in weather between 2014 and 2015.