Hollow Heart of Watermelon
» Hollow heart of
» Watermelon varieties with dense fruit flesh are less susceptible to hollow heart.
» Hollow heart is more common on fruit that is set early in the season.
2). Hollow heart affects watermelon production throughout the world, and the condition lowers the marketability of the fruit resulting in millions of dollars of losses each year
The research at the University of Delaware found that there was no hollow heart in a hollow susceptible variety when adequate ratios and spacing were used. However, when the distance from plants to plants increased, the incidence of the hollow heart increased. Plants located five feet away from a plant showed a hollow heart incidence of 56%, and plants located eight feet away from a had a 74% incidence. A follow-up study found that decreasing the ratio of plants in the planting of watermelons was associated with an increase in the incidence of hollow heart.
Cause of Hollow Heart
In the past, it was thought that varying soil moisture and excess nitrogen levels were the causes of hollow heart. However, research at the University of Delaware has shown that the primary cause of hollow heart is inadequate pollination.1 This explains why hollow heart occurs more frequently on triploid (seedless) varieties.
Fruit set on
Inadequate pollination can result from (1) not enough pollen produced on the polleniser plants, (2) inadequate rates of pollen transfer to female flowers, or (3) low pollen viability
The incidence of hollow heart tends to be higher on early set fruit (fruit closest to the crown). Cooler temperatures and a higher frequency of storms early in the season suppress the activity of pollinators (honey bees).3,5,7 Cold weather is also associated with reduced pollen viability and reduced rates of pollination
There is also variation
The process of fruit expansion is affected by the rate of pollination and the characteristics of the watermelon variety. Varieties with longer fruit (a length
and orange flesh varieties also tend to have higher levels of hollow heart than do red-flesh varieties.3 There may be some association of hollow heart with soil moisture and nutrient levels, as these factors play a role in fruit expansion rates.
Growers can choose less susceptible varieties with higher density flesh to minimize problems with hollow heart. Growers can also take steps to improve pollination rates, including using the appropriate
Growers should supply the appropriate number of honey bee hives for the size of the watermelon planting, and place the hives in several locations around the field. Consider using bumblebees for pollination during periods of cold weather.
1 Johnson, G. 2014. Watermelon pollination, fruit set, and hollow heart. Weekly crop update. University of Delaware. https://sites.udel.edu/weeklycropupdate/?p=6579. 2 Trandel, M., Perkins-Veazie, P., Schultheis, J., Gunter, C., Johanningsmeier, S., and Johannes, E. 2019. Presentation at the ASHS Annual Conference. 3 Guan, W. 2018. Hollowheart of watermelons. PPDL Picture of the Week. September 4, 2018. Purdue Agriculture, Plant and Pest Diagnostic Laboratory. https://ag.purdue.edu/btny/ppdl/Pages/POTW2018/POTW09042018.aspx.
4 Thomas, A. 2015. Researcher finds potential cause of hollow heart disorder in watermelons. Phys.Org. June 19, 2015. https://phys.org/news/2015-06-potential-hollow-heart-disorder- watermelons.html. 5 Thomas, A. 2015. Saving watermelons. UD Daily. University of Delaware. http://www1.udel.edu/udaily/2015/jun/watermelons-061815.html. 6 United States Standards of Grades of Watermelon. USDA-AMS. Effective March 23, 2006. https://www.ams.usda.gov/ grades-standards/watermelon-grades-and-standards. 7 Johnson, G. and Ernest, E. 2011.
Conditions influencing hollow heart disorder in triploid watermelon. ASHS Annual Conference. https://www.researchgate.net/publication/267277292_Conditions_Influencing_Hollow_Heart_ Disorder_In_Triploid_Watermelon. 8 Walters, A. 2005. Honey bee pollination requirements for triploid watermelon. HortScience 40:1268-1270. 9 Kano, Y. 1993. Relationship between the occurrence of hollowing in watermelon and the size and the number of fruit cells and intercellular air spaces. Journal of the Japanese Society for Horticultural Science 62:103-112. 10 Freeman, J., Miller, G., Olson, S. and Stall, W. 2007. Diploid with watermelon pollenizer cultivars differ respect to triploid watermelon yield. HortTechnology 17:518-522.
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