New Soybean Rust Host Found in U.S.

By Aine Gianoli
DTN Staff Reporter

TORONTO (DTN) -- A sample of coral bean has tested positive for Asian soybean rust.

"It's a new host for the continental United States," Carrie Harmon, a University of Florida plant pathologist and associate director of the Southern Plant Diagnostic Network, told DTN Friday. No Asian soybean rust had been found on U.S. coral bean before, but closely related plants have infected with the other species of rust in Puerto Rico.


"It (coral bean) is widespread in Florida and possibly in other southern states," she said. Coral bean is blooming in Florida right now and can be observed along roadsides, old homesteads, abandoned lots and gardens. The plants, which are about 3 feet tall, have bright red flowers, which are flowering everywhere right now, Harmon said. "The bright red beans are noted when the pods dry in the fall."

A possibly infected sample of Erythrina herbacea, commonly known as coral or Cherokee bean and part of the Fabacea -- pea -- family, was found in a central Florida kudzu Asian soybean rust sentinel plot that is monitored year-round and sent for testing in at the National Plant Diagnostic Network hub lab in Gainsville, Fla. Monday.

The sample tested positive. A positive ASR find on a new host means the sample must then be sent on for federal testing so the coral bean sample headed north to USDA's Systematic Mycology and Microbiology Laboratory in Beltsville, Md., for three tests.

The results of the first test were positive so a preliminary confirmation has been made, Harmon said. The first federal test confirms the Florida testing.

The coral bean infection will be reported on USDA's Pest Information Platform for Extension and Education website, commonly known as PIPE, which tracks ASR and soybean aphids.

"I'll be working with the PIPE folks to get this on there," Harmon said. It may be added under kudzu/other wild legumes, rather than its own category, but the specifics of the find will be listed under the commentary section.

Asian soybean rust scouts are now scouring Florida in search of more coral bean samples.

"So far, we just have it (rust on coral bean) in this one site," Harmon said.

Coral bean was not being checked previously for rust. "We weren't looking at it before," Harmon said. ASR "is a strange rust," she said. "Most rusts go to one host ... it's been noted on a long list of hosts."

Little is known about the implications the plant could have on rust infections in the U.S. Until more samples are found, scientists won't know how long coral bean holds its leaves during the season, disease incidence and severity, interaction with kudzu and soybeans, and other specifics.

"I can't give you any real implication information," Harmon said, because they know little about how the plant and the disease will interact. "This is one we're just going to have to watch this season."

Coral bean can survive the winter in frost-free areas, such as central Florida and south of Tampa; in areas where it survives the winter, the plant can grow to be 10 feet to 12 feet tall. The plan has large tuberous roots that are "huge, the size of a softball," Harmon said.

The plant dies to the ground in winter, during which "survival is virtually nil. It doesn't have any green tissue during the winter time" north of Tampa, she said. The Florida panhandle receives several frosts per year, so it may regenerate from underground parts, Harmon said.

Coral bean is considered native to Florida, but Harmon said to keep in mind the nuances of the term "native." Some people define a plant as native if it has been in a location for more than 100 years; others define it as native if it was in the location when first documented by explorers.

"It is sold in garden catalogs as an ornamental," Harmon said. "It is a desired ornamental" and hummingbirds like it, but it is toxic to humans.

Aine Gianoli can be reached at aine.gianoli@dtn.com.

Copyright DTN 2008. All Rights Reserved.