Using biotechnology and pest-management tools, researchers at the University of California, Davis, helped re-establish the Dominican Republic tomato processing industry after a deadly tomato virus wiped it out in the 1990s. They hope a similar strategy could be successfully employed in the United States.

With origins in the Old World, the tomato yellow leaf curl virus (TYLCV) is spreading throughout the southeastern United States and could one day threaten California agriculture. The insect that spreads the virus -- the silverleaf whitefly -- is well established in the state.

"Our research addressed a number of issues, including invasive species, application of biotechnology to solving an important practical problem and the preservation of an important industry for low-income small farmers in a less developed country," said Robert Gilbertson, a professor in UC Davis' plant pathology department.

The Dominican Republic is a small Caribbean island nation of almost 8 million people and home to a non-export tomato industry that involves hundreds of small farmers and thousands of workers -- and feeds many more.

In the early 1990s, Dominican farmers began noticing that some tomato plants were suffering from severe stunting, yellowing, reduced leaf size, and significant yield reduction -- all symptoms of the tomato yellow leaf curl virus. By 1994, the entire tomato crop had been destroyed, amounting to losses of millions of dollars and severe economic hardship for farmers and farm workers. Dominican canneries resorted to importing bulk paste from other countries.

By examining the genetic material of the virus from tomatoes in the Dominican Republic, Gilbertson and other scientists hoped to precisely identify the virus infecting the tomato crops. Their research confirmed their worst fears -- somehow, the virus had hopped the Atlantic and arrived in the Dominican Republic.

Along with University of Wisconsin researcher Doug Maxwell, Gilbertson used biotechnology to clone the genetic material of the virus and determine the complete sequence of the viral genetic material or DNA. Tests indicated it was 97 percent identical to the TYLCV found in eastern Mediterranean countries.

"The 'mother of all tomato viruses' had been inadvertently introduced to the Dominican from the eastern Mediterranean, and the Dominican whiteflies were able to spread the virus rapidly," Gilbertson said. "The virus is not carried in seed, so it was most likely smuggled in with tomato plants brought in from a location where the virus occurred."

He and officials from the Dominican Republic Ministry of Agriculture and the tomato industry developed an integrated pest management plan to rejuvenate the tomato industry. First, a three-month, host-free period was implemented. That means that the crops on which the whitefly lives -- tomatoes, peppers, beans, melons -- were not allowed to be grown in the tomato-production areas.

The government agreed to enforce the controversial policy, which scientists considered critical.

"We then used biotechnology and our knowledge of the genetic sequence of the virus to develop a polymerase chain reaction (PCR) test that would indicate whether the whiteflies were carrying the virus or not," Gilbertson said. "We wanted to know if the amount of virus carried by whiteflies decreased during the host-free period -- and it did."

The researchers found that during the tomato season, all whiteflies tested carried the virus. However, during the host-free period, the number of virus-carrying whiteflies dropped to almost nil.

Next, researchers led by Donald May, a UC Farm advisor in Fresno County, helped identify new early-maturing hybrid tomatoes designed to produce good yields before the virus built up after the host-free period. Finally, in some cases, insecticides were used, including a new type with low mammalian toxicity.

Using this integrated pest management (IPM) approach, the Dominican tomato industry slowly began to rebound. By 1999 the nation no longer had to import tomato paste, and the next year the tomato crop was the largest on record. Gilbertson and his colleagues were honored with a special award from the secretary of agriculture in the Dominican Republic for their assistance in the management of the tomato yellow leaf curl virus.

"This project illustrates what can be done when the tools of biotechnology -- and not necessarily genetically modified organisms -- are applied to a practical problem," Gilbertson said. "Working together, researchers from U.S. universities, the Dominican Republic government and private industry were able to manage a devastating disease problem."

In 1997, the same tomato virus was found to have spread into Florida from the Dominican Republic or another Caribbean island. The virus has now been detected in Georgia and Louisiana, as well as other Caribbean countries.