USF Virus Hunters Tackling Plant Disease


DNA sequencing of the lowly whitefly will give scientists an edge in fighting crop damage.


By Vickie Chachere

USF News


ST. PETERSBURG, Fla. (April 22, 2011) – USF researchers have developed a new technique to identify potentially crop-killing viruses before they strike by hunting for unknown viruses using both the lowly whitefly and advanced DNA-sequencing techniques.


The research conducted at USF’s College of Marine Science has the potential to stop crop outbreaks before they happen by identifying damaging viruses circulating in the region, said Mya Breitbart, whose virus-hunting laboratory has been at the forefront of creating new surveillance techniques. The research was published in today’s edition of the journal PLoS One.


The new technique uses the tiny whitefly, a ubiquitous pest that’s widely found in Florida farms and is a known carrier of plant viruses, to identify what types of viruses are prevalent in any given field.


Instead of sampling individual diseased plants, the researchers collected whiteflies, purifying and sequencing the viruses they carry. The method can identify known viral pathogens, as well as new viruses that were not previously known in the area or known at all.


The method also can identify viruses of nearby weeds. That’s important because scientists do not know much about viruses in weeds but weeds are important reservoirs for generating new viruses that turn into emerging pathogens that can damage crops, Breitbart said.


In their research, the scientists developed a new technique called “vector-enabled metagenomics” to discover which viruses the whiteflies were carrying. The viruses were purified and their DNA then sequenced and run against a database of known virus DNA to identify the type.

Whiteflies often occur in high populations on many crops especially at the end of the production cycle when farmers are withholding insecticide applications as they ready the harvest. Whitefly vectors are natural “flying syringes” that can sample viruses from many individual plants and different plant species over space and time, Breitbart noted.


 “By enabling the discovery of a wide range of viruses and satellites, VEM is a powerful technique that will significantly enhance our fundamental scientific understanding of plant viral diversity, biogeography, and emergence,” the group wrote in the PLoS One article.


“Typically, new plant viruses are not identified until an outbreak causing significant crop loss occurs. This has put agricultural biodefense into a reactive mindset – waiting until a new disease becomes a problem before trying to understand and combat the causative agent.”


In their study, VEM successfully characterized the active and abundant viruses that produce disease symptoms in crops, as well as the less abundant viruses infecting adjacent native vegetation.


Adult whiteflies (Bemisia tabaci) were collected using battery-operated vacuums from two fields in Citra and Homestead. The Citra sample contained whiteflies collected from soybean and watermelon plants in August 2007, while the Homestead sample was collected in April 2009 and contained whiteflies from tomato and squash plants in the vicinity of mixed cucurbit crops such as cantaloupe, pumpkin, cucumber, and watermelon.


Vegetable crops in Florida have experienced significant losses due to whitefly-transmitted viruses over the past 15 years. The dominant viruses identified in this study were Tomato yellow leaf curl virus and Cucurbit leaf crumple virus, which are both whitefly-transmitted viruses that have been introduced to Florida since the arrival of the silverleaf whitefly in the late 1980s.


The researchers also identified two never-before-seen viruses which appear to be most closely related to Desmodium leaf distortion virus and part of a group that includes Cotton leaf crumple virus, Sida yellow leaf curl virus and Tomato severe leaf curl virus. Since none of these viruses have been previously reported in Florida, studies are underway to more fully characterize them, Breitbart said.


The research was conducted by former USF PhD student Terry Fei Fan Ng, who has since joined the Blood Systems Research Institute in San Francisco; Siobain Duffy of Rutgers University; Jane E. Polston and Gary Vallad of the University of Florida, and Elise Bixby and Breitbart of USF.


The study was funded through the U.S Department of Agriculture’s Tropical-Subtropical Agriculture Research (T-STAR) program and the National Science Foundation’s Biodiversity Inventories program.


Vickie Chachere can be reached at 813-974-6251.