Research key to pomegranate success

Oct 01, 17 Research key to pomegranate success

By Vicky Boyd

Florida’s fledgling pomegranate industry will continue to sprout, growers and researchers say, although work remains to be done in managing the diseases that plague pomegranate trees.

After 10 years of conducting trials into suitable varieties and related cultural practices, Bill Castle remains optimistic, and research at the University of Florida’s Citrus Research and Education Center in Lake Alfred is tackling some of the challenges. Castle is a horticulture professor emeritus at the center.

At the outset of his research, Castle said, “I realized that diseases — not insect pests but diseases — were going to be a problem, and we can’t develop a commercial industry until we understand what the disease problems are and how to manage those. I think that is still true today.”

Cindy Weinstein, president of the Florida Pomegranate Association and owner of Green Sea Farms Pomegranate Nursery in Zolfo Springs, said she also remains hopeful.

“Yes, we do have hurdles to jump over. But yes, it’s doable, and we’re getting fruit. Our biggest handicap is getting (fungicide) labels,” she said.

Although Weinstein said she expects that the pomegranate industry will serve local and regional fresh fruit markets initially, she hopes it eventually grows large enough for international markets and related processing, cosmetic and pharmaceutical industries.

Pomegranates are not new to the state, with a small industry dating back to the late 1800s. With the challenges facing the Florida citrus industry and changing consumer tastes and nutritional demands, Weinstein said, pomegranates have seen a resurgence of interest from growers.pomegranate-fruit-and-flowe

Know thine enemy

About four years ago, Castle enlisted the help of Gary Vallad, an associate professor of plant pathology at the UF Gulf Coast Research and Education Center in Balm, to identify pathogens and develop ways to manage them.

“Bill came to us because he was having issues with several diseases that were severely limiting his ability to assess their varieties,” Vallad said. “There are a lot of varieties that would do well in Florida if it weren’t for the diseases.”

With the aid of a specialty crop block grant, Vallad began surveying pomegranate plantings to identify diseases and determine which ones were economically important. He found Colletotrichum was causing the most economic damage, followed by Botryosphaeriaceae – nicknamed Bot — and a few others.

“The most important pathogen that’s out there by far is Colletotrichum,” Vallad said, referring to the organism also known as anthracnose. Not only does it cause blossom blight, fruit rot, leaf spots, shoot blight, twig cankers and defoliation, but in severe cases it can cause branch dieback.

Based on that newfound knowledge, Vallad and his colleagues began conducting trials on cooperating growers’ infected trees. Only a few conventional products are registered for use on pomegranates, and they’re mostly for post-harvest diseases. Instead, the researchers focused on fungicides already registered for use on other fruit crops.

A handful of products proved effective, and Vallad said they have worked with the IR-4 Project, which helps develop data to support new Environmental Protection Agency tolerances and labeled uses for minor-use crops. The trials also showed that applying a fungicide at bloom is the most important, Vallad said. Repeating applications at other times of the year didn’t significantly improve disease control.

Building on Castle’s work, Vallad also found that removing dead leaves, diseased branches and rotten fruit on which spores can overwinter are critical to an integrated disease management program.

Growers have taken note, Weinstein said.

“Our trees were infected with fungus, but because of research at GREC we now know what type of fungus we have and been able to clean up our trees for marketable pomegranates,” she said.

In addition, Vallad and his group are trying to determine if there are other hosts for the disease. Because Colletotrichum also affects citrus and blueberries, does having a pomegranate orchard near those crops increase the potential for or severity of infection?

“This becomes really important, because we have a lot of folks who are blueberry growers or citrus growers,” he said.

Breeding for success

As part of the block grant, Zhanao Deng, UF professor of ornamental plant breeding and genetics based at GREC, began a breeding program to develop varieties that could perform well in Florida’s climate and disease pressures. At the same time, the trees had to yield tasty fruit consumers will want.pomegranates-closeup-resize

Deng started with about a dozen different cultivars, including Wonderful, the most widely grown variety in California. He screened the seedlings, selecting for desirable traits. The young trees eventually were planted in a 3.5-acre orchard at Balm and will act as a material source for future breeding.

Another part of the research, led by GREC agricultural economist Zhenfei Guan, involves examining the economics of growing pomegranates.

Shinsuke Agehara, an assistant professor of horticultural sciences at GREC, received a separate specialty crop block grant to study and improve pomegranate tree nutrition.

“It seems pomegranates are really heavy feeders, and people weren’t feeding them nearly enough,” Weinstein said.

For more information, visit UF’s pomegranate website at http://www.crec.ifas.ufl.edu/extension/pomegranates/.

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