Progress 09/15/03 to 09/14/05
Two strains of the plant pathogen, Xylella fastidiosa, have resulted in severe economic losses in Central and South America. Citrus Variegated Chlorosis (CVC) is currently widespread throughout South America and Central America and Coffee Leaf Scorch (CLS) is predominant in Central America. Both strains threaten agriculture within the Caribbean and Caribbean islands also may be a gateway for the spread of CVC into South Florida resulting in severe economic losses to the mainland Citrus industry. Previously, the status of Xylella within the Caribbean had not been examined. We sampled citrus and coffee intensively throughout Puerto Rico in 2004 and 2005 throughout the year (four collection trips per year). All plant samples of citrus, coffee and adjacent host plants were found to be negative for Xylella by molecular techniques (PCR) and culturing. Other endophytic bacteria that can potentially interact with Xylella were identified from both coffee and citrus. The status
of potential vectors (sharpshooter leafhoppers and froghoppers) was also assessed by use of traps and sweeps. Over 3,000 leafhoppers were collected each year and identified to species if potential vectors (sharpshooters or froghoppers) or to family if they were other types of leafhoppers. Four sharpshooter species were found within coffee and citrus plantings. The most abundant species was Hortensia similis which is widespread throughout the island and abundant throughout the year. Caribovia coffeacola was abundant in coffee plantings, but only at higher elevations. Both H. similis and C. coffeacola feed primarily on grasses, but each species was also observed feeding on both coffee and citrus. Two other sharpshooter species and five species of froghoppers were collected within coffee and citrus plantings but only on rare occasion. The abundance of H. similis and C. coffeacola suggests that Puerto Rico has insects capable of vectoring Xylella if it is introduced, but Puerto Rico lacks
the larger sharpshooters that are more efficient vectors for Xylella transmission in North and South America. Sharpshooters were also assayed for Xylella; all were negative. Puerto Rican researchers learned the necessary technology so that they can continue to monitor the Xylella status of Puerto Rico after termination of this current project. Subsequent research will focus on the behavior, ecology and vectoring capacity of the sharpshooter species that are abundant within Puerto Rico.
Our studies confirm that Xylella fastidiosa is currently not widespread in coffee and citrus in Puerto Rico. All samples examined during 2004 and 2005 tested negative for Xylella. The mountainous topography of Puerto Rico results in many isolated plantings of coffee/citrus at high elevations, and thus we cannot say conclusively that some coffee and/or citrus is not infected within Puerto Rico. During the time of this study new strains of Xylella increased their range in South and Central America; the Caribbean is nearly circumvented by lands harboring Xylella. Puerto Rico imports a great percentage of their agricultural goods for consumption, thus allowing possible introduction of Xylella in plant material. Hurricane activity increased dramatically during 2004 and 2005 thus increasing the possibility of wind borne introduction of Xylella on insects or on plant material. Our studies also established that two potential vectors, Hortensia similis and Caribovia coffeacola,
are common within coffee and citrus plantings and that both leafhoppers will feed on both coffee and citrus. For all of these reasons, it is essential that the status of Xylella continue to be monitored within the Caribbean. One of the primary benefits of this project is that the technology for identifying, isolating, and culturing Xylella has been forwarded to researchers in Puerto Rico. Identifying the spread of Xylella in the Caribbean is essential to protecting the coffee and citrus industries in Puerto Rico as well as the Citrus industry in the mainland United States.
- No publications reported this period
Progress 10/01/03 to 09/30/04
Leafhopper populations were sampled at six field sites containing citrus and coffee in Puerto Rico during February, May and August of 2004. Sampling was by sweeping and sticky traps left at the sites for 3 to 4 days. Approximately 40 different species of leafhoppers were collected and are currently being identified. The two most common sharpshooters (potential Xylella vectors) were Hortensia similis and Caribovia coffeacola. Both species were more commonly found feeding on grasses surrounding coffee and citrus, although both were periodically collected directly off of both plant species. Different species of froghoppers (also potential vectors) were collected and are being identified. The froghopper Leocomiopsis scaramuzzai was found actively feeding on xylem of the hardwood Ficus laevigata, and thus should be considered a candidate for Xylella transmission. Hopper populations were highest in May and appear more diverse and abundant on coffee than on citrus.
Collections were also made in forests surrounding mountain plantings of coffee and citrus; these populations showed even greater diversity as we would expect with the high plant diversity in these forests. On each sampling dates we also collected plant material from citrus and coffee that appeared symptomatic for the presence of Xylella (symptoms of citrus variegated chlorosis or coffee leaf scorch). Many plants appeared symptomatic during the dry season (February and May), but it is difficult to visually detect Xylella as coffee/citrus in Puerto Rico receive no irrigation and many plants appear stressed during the dry season. Thus far no plant samples have tested positive for Xylella by culturing and PCR performed to date. Other xylem-inhabiting bacteria have been found, however, and are being identified by PDs Zapata and Hartung. We will continue to test coffee and citrus for Xylella in 2005, but will also examine alternative hosts that may harbor Xylella. Species of milkweed and
other weedy hosts are often found in coffee plantings and are fed upon heavily by leafhoppers. In addition, we will test the sharpshooters H. similis and C. coffeacola directly for the presence of Xylella.
We will decribe the diversity of xylem feeding leafhoppers in Puerto Rico. We will also test the presence of different strains of Xylella fastidiosa in plants and in insects in Puerto Rico. This information is of extreme significance to Florida's citrus industry as plants in the Carribean may be a source of Xylella strains such as citrus variegated chlorosis.
- No publications reported this period