By H.R. Pappu, D.B. Langston, J.T. Flanders, and D.G. RileyWhile Georgias tomato and pepper growers are trying to deal with tomato spotted wilt, another potentially serious disease of tomato just entered state.
Tomato yellow leaf curl virus is a gemini virus and caused serious economic losses to tomato growers in the Caribbean and Florida. The disease has been present in Israel for over 40 years and then appeared in
Cuba, Jamaica and the Dominican Republic in the early 90s. Soon after, it became the biggest constraint to tomato production in Dominican Republic. In July 1997 symptomatic plants were first seen in Dade County,
FL. The virus got established quickly and tomato growers in Florida began seeing its economic impact soon after.
The virus is transmitted by sweet potato and silverleaf whiteflies. Infected plants often
display characteristic symptoms. Early infection leads to severe stunting of the plant with virtually no yield at all. Other symptoms include chlorosis along the leaf margins, and upward cupping (hence the name,
leaf curl). The virus has a wide host range although tomato is one of the primary crops affected. Recently there is a report from Mexico that pepper is also susceptible to the virus.
As the disease is
well-established in Florida and with the climate in the southeast conducive for the build up of whitefly population, it was thought that it was only a matter of time before the disease showed up in Georgia. In
1998 Fall season, symptomatic tomato plants were noticed in Decatur County, GA and the disease was estimated to be less than 1%. During 1999 Fall, reports of the disease came from Grady, Colquitt and Tift
Counties. Some fields in Grady County had as much as 15% infection. In the experimental plots in Tift County, infection in individual plots ranged from 15 to 90%. This sudden outbreak of the disease
may be attributed to relatively large populations of the whitefly vector in south Georgia.
While the virus causes distinct and characteristic symptoms on tomato, diagnosis may often need to be verified using
laboratory tests since other tomato-infecting geminiviruses produce similar symptoms. There is no reliable and virus-specific serological test available. In order to confirm the virus infection, a
DNA-targeted method called polymerase chain reaction is being used. Using this method, the genetic material of the virus (in this case, DNA) is detected in the plant sample. This technique is highly
sensitive and we are able to improve the procedures involved in preparing the plant material to minimize the time required in completing the test.
It is difficult to predict the potential future impact of this disease
on Georgias tomato crop. Judging from its track record in other countries and in Florida, it can lead to yield reduction. While it is impractical to completely eradicate a vector-borne virus disease, a combination
of production practices may minimize the impact of the disease. These include using disease free transplants, roguing the infected plants (early in the season), and managing whitefly populations using various
insecticides.
The most effective and durable management strategy would be growing leaf curl-resistant cultivars. Most of the progress in identifying sources of resistance in relatives of cultivated tomato has
been made in Israel where scientists have been working on breeding new resistant varieties.
We continue to monitor the disease situation closely in the coming seasons and conduct research to better understand and
control the disease.
