Quick action thwarts tomato virus

EDITOR'S NOTE — The following article first appeared in the winter edition of Impact magazine which is published by the University of Florida's Institute of Food and Agricultural Sciences.

When a new virus that could ruin the state's 50,000 acre tomato industry was discovered in 1997, a team of University of Florida research and Extension faculty moved quickly to prevent the virus from becoming a major threat to Florida agriculture.

Tomato yellow leaf curl virus, or TYLCV, which prevents plants from producing marketable tomatoes, was first discovered in Charlotte, Collier, Miami-Dade and Sarasota counties, but it's now a statewide problem, said Jane Polston, associate professor of plant pathology at UF's Gulf Coast Research and Education Center (REC) in Bradenton.

“Spread rapidly and efficiently by whiteflies, the virus causes limited tomato production in other areas of the world wherever it becomes established,” Polston said. “It also infects weeds and other crops such as green beans and ornamentals.”

Key symptoms of the virus include severely stunted plants with deformed leaves showing yellow leaf margins. Leaves are reduced in size and may be cupped. Infected plants have a bushy appearance, but they lose vigor, drop flowers prematurely and have little or no fruit set.

First identified in Israel in 1959, the virus spread to Mediterranean and Caribbean countries. In 1992, it destroyed 90 percent of the tomato crop in the Dominican Republic. Polston said the virus probably entered the United States on infected plants, or it may have been carried by whiteflies from the Caribbean.

Polston, who discovered the virus on small tomato plants being sold to consumers at retail nursery stores, immediately recognized the potential impact of the virus on the state's tomato production and transplant industries and moved quickly to organize a rapid response to the threat.

Five days after the virus was discovered in Florida, the UF Extension Service notified all tomato growers in the state about the problem. To deal with various aspects of the problems, an 11-member team was established by UF's Institute of Food and Agricultural Sciences to work closely with growers, as well as the Florida Department of Agriculture and Consumer Services and the U.S. Department of Agriculture. The UF team includes faculty in entomology, plant pathology and horticultural sciences.

“Members of the team quickly assessed the prevalence of the virus in tomato transplants sold in the retail trade and in commercial production fields and worked with state regulatory officials to stop the movement of the virus within and out of the state,” she said.

And they developed an on-going research and Extension education program to identify and control the whitefly vector, understand the epidemiology of the virus, minimize its spread and keep growers informed of the latest information on virus management. These actions were completed within two months of the first identification of the virus in Florida.

In addition to Polston, members of the team include: Phyllis Gilreath, Manatee County Extension agent, Bradenton; Earnest Hiebert, professor, Department of Plant Pathology, Gainesville; Mary Lamberts, Miami-Dade County Extension agent (vegetables), Homestead; Gene McAvoy, Hendry County Extension agent, La Belle; Robert McGovern, associate professor of plant pathology, Gulf Coast REC, Bradenton; David Schuster, professor of entomology, Gulf Coast REC, Bradenton; John Scott, professor of horticulture, Gulf Coast REC, Bradenton; Kenneth Shuyler, Palm Beach County Extension agent (vegetables), West Palm Beach; Philip Stansly, professor of entomology, Southwest Florida REC, Immokalee; and Suzanne Stapleton, Suwannee County Extension agent, marketing, Live Oak.

Glenn Dickman, owner of Artesian Farms in Ruskin, said the state's tomato industry would have been devastated without UF's prompt response to the problem. “Without UF's quick and vigilant action, the virus had the potential to cause great losses in tomato production throughout Florida and make transplants produced in Florida unmarketable outside the state,” he said.

“Without their help, the state's transplant industry would have faced economic boycott from other states that import Florida-grown vegetable and ornamental transplants.”

Dickman also said the absence of effective management strategies would have led tomato growers to apply excessive amounts of insecticides and herbicides in their efforts to reduce the virus in their fields.

“I can't say enough good things about the UF team and how they have helped us deal with whiteflies and the viruses they spread,” said Joe Mobley, operations manager for Artesian Farms.

“Like many growers, we simply did not understand the disease and how it is spread by whiteflies, but the team — particularly David Schuster and Phil Stansly — has helped us minimize our losses by bringing the whitefly under control with pesticides,” Mobley said. “UF has been very helpful in our cultural practices, which include everything from selecting the right plastic mulch to cleaning up nearby fields that harbor whitefly populations and using so-called trap crops to control this pest,” he said.

Reggie Brown, manager of the Florida Tomato Committee in Orlando, said rapid identification and response to the TYLCV problem is another example of UF's valuable research and Extension programs.

“The quality of the Extension agents working with the tomato industry is superb,” he said. “They are in the field interacting with the producers on a daily basis and provide that early warning system that is essential to combating new pests. A strong focus on solving ‘real problems in real time’ with good communication throughout the system gets results.”

Polston said other recent accomplishments of the team include the development of new tomato breeding lines by Scott and Schuster that are resistant to TYLCV as well as a less troublesome virus, tomato mottle virus.

In 1998, Polston and Hiebert initiated a research project to identify genes from the virus that could be inserted into the tomato and used to provide resistance to TYLCV. They have found at least one that makes the tomato plants immune to TYLCV.

“We are very pleased with the results, since this is the only known source of immunity to TYLCV,” said Hiebert. “Our goal now is to get this gene into commercial hybrids.”

In addition, four TYLCV-resistant cultivars that became available in 2000 from two seed companies were screened for horticultural performance and virus resistance at three Florida locations: Bradention, Homestead and West Palm Beach. The tests were conducted by Gilreath, Polston, Shuler, McAvoy and Stansly.

The UF group received the IFAS Research and Extension Team Award at the Florida Associations of Extension Professionals Conference in West Palm Beach last fall.

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