What’s the buzz on seedless watermelons? It’s all about pollen say UD researchers

If you are looking for a watermelon seed spitting contest this summer, you might be out of luck!

siefrit and johnson kneeling by watermelon row
UD grad student Donald Seifrit, Jr. and Gordon Johnson, fruit and vegetable Extension specialist conduct seedless watermelon pollination trials

Most Delawareans, like the rest of Americans, prefer their watermelons seedless-a trend that began to take hold in this country about 10 years ago.

round watermelon
Fascination, a popular seedless watermelon variety in Delaware
Super Seedless-7187, a popular seedless watermelon grown in Delaware
Super Seedless-7187, a popular seedless watermelon grown in Delaware

Gordon Johnson, Extension vegetable and fruit specialist and UD graduate student Donald Seifrit, Jr. are helping growers meet that demand.

They are beginning the first year of a two year trial to examine 24 pollination companions for two popular seedless watermelon varieties, Fascination and SS-7187 (SS = super seedless), grown in Delaware. MarDel Watermelon Association provides funding support for the study. Seifrit’s stipend is made possible by a specialty crop block grant from the Delaware Department of Agriculture and USDA.

In order to grow the seedless watermelons preferred by the public, a seeded ‘pollenizer’ watermelon with male flowers must be a companion to the seedless plants, whose pollen is not viable. For this study, one male watermelon plant is paired alongside three seedless plants. “The pollen to produce a seedless watermelon has to come from a seeded plant” Johnson said.

Johnson and Seifert will seek to determine what affects pollination, and observe which pollenizer varieties attract more bees, all of which in turn might increase or influence fruit set.

Eight rows of the summer fruit, with their tendrils spanning across neat rows covered in black plastic, are spread out over a four-acre research plot. Space between the watermelon rows is an important barrier so that pollen-seeking bees won’t jump to another row and another varietal source of pollen. Bees tend to fly along the rows however. With the watermelons rows effectively isolated, bee preferences can be observed with a “high probability of accuracy.” Non-pollen sources are also planted in between the watermelon rows to further isolate the pollen movement and preserve the integrity of the observations.

Johnson and Seifert brought in six hives to pollinate the crop.  Wild bees also help pollinate. As the bees travel up the rows, Johnson and Seifert will record the bee’s patterns. “A plant with more pollen and better nutrition will attract more bees.” Johnson said. After the trial studies are complete, Johnson will make the results available to area growers, who can adapt the research to obtain better pollination, fruit set and yields.

rows of watermelon plants
Two seedless watermelon plants are matched with one of 24 seeded varieties, needed for pollination

Watermelons grown on the eastern shore come to local market in time for the Fourth of July holiday. Watermelon availability begins in the southern states and moves up the East Coast as spring turns to summer, Johnson said. Watermelons consumed over the Memorial Day weekend, likely came from Florida, Johnson said.

For Delaware farmers, watermelons are an important crop and livelihood. Together as part of the Eastern Shore region, approximately 5,000 acres are devoted to growing watermelons. Together with Indiana, Delmarva farmers produce the majority of watermelons that are consumed on the East Coast from mid-July to Labor Day.

Johnson is looking to improve early fruit set for local growers. That means more local watermelons for consumers and better profits for growers. “The earlier the fruit set, the better,” Johnson explained.

“Typically, you get two watermelons per plant at any time,” Johnson said. “If it is really good, we will get three.”

“The other things we are looking at are the environmental effects on pollen viability. As the plants mature, Seifrit will also test their sweetness and firmness levels.

“We are trying to find out ways to improve fruit set in general and early fruit set in particular,” Johnson said. “We’re looking for the best combinations of pollinators for early set.

Watermelons are an expensive crop to grow, Johnson remarked. An earlier fruit set improves a farmer’s return on their investment.

Watermelons are a native desert plant, Johnson said. “They like heat and tolerate dry conditions, but to obtain good yields, farmers must irrigate well.” Watermelon crops require rotation and careful monitoring. As members of the Cucurbitaceae family that grow at ground level, they are more prone to pests and diseases than other crops. To grow successfully, farmers must invest in apiaries. Some growers use bumble bees, but honey bees are more common, Johnson said.

Siefrit is exploring the possibilities of obtaining special bee video gear in order to better track bee preferences and behavior.

Unsuccessful pollination can result in other problems.

In earlier studies, Johnson and his team made a discovery – the mechanism for Hollow Heart, a condition that leaves the core of the watermelon fruit hollow. “We haven’t had much of a problem here in Delaware, because of all the varieties, but other states have had bad problems,”Johnson added. “We are pretty convinced it is a lack of pollen, or incomplete pollination. Don is taking that research to the next level – cutting open baby watermelons and counting cells.” Johnson said.

“We are looking what affects pollen – if it is cold, if bee flight is down or if there is a loss of bees,” Johnson said. Logistics is important too, Johnson added. Growers must coordinate planting pollenizers with their seedless plants. If the seedless varieties are more long in shape, the seedless watermelons will need to be round in shape, and vice versa. This helps to tell them apart as they go to harvest.

Johnson said most requests for seeded watermelons in Delmarva come from new ethnic populations and “seeded watermelons are what they are used to.”

“The rest of the world, with the exception of Japan and some production in southern Europe, really prefers seeded varieties,” Johnson remarked. ” Eighty percent of the world’s watermelon crop is seeded.” But in Delaware, 90 percent of the watermelons grown are seedless.”

>>>Information on UD Extension’s Small Fruit and Educational Tour – July 10, 2014

Article by Michele Walfred
Photos by Jackie Arpie