Survey of bacterial leaf scorch incidence in southern highbush blueberries in Georgia

Summary

In 2008, UGA extension specialists, researchers, and county agents initiated a survey to determine the prevalence of bacterial leaf scorch in Georgia's major blueberry production region, as well as whether or not resistance is present among some southern highbush cultivars. The most valuable initial information derived from this survey is the determination of the degree of susceptibility of various cultivars. It does appear that resistance or tolerance does exist among some cultivars, and producers can now use this information to select resistant cultivars. In addition, breeders now need to breed for cultivars which are resistant to this disease.

Situation

Relative to total sales, blueberries have quickly grown to be the number one fruit commodity in the state, surpassing even peaches. Recently, a new disease has been identified in the Georgia blueberry production region. This disease has been named bacterial leaf scorch, and it is caused by the xylem-inhabiting bacterium Xylella fastidiosa. To date, the disease has been predominantly a problem of southern highbush blueberry varieties. The initial symptom is a marginal leaf scorch. This leaf symptom can be uniformly distributed throughout the plant, but in the early stages, scorching may be limited to individual stems or perhaps one side of the plant – indicating that only a partial xylem blockage has occurred that may be limited to one cane or one stem. Eventually, leaf drop occurs, and young twigs/stems may take on a yellow appearance. After leaf drop, the plant eventually dies.

Response

In 2008, UGA extension specialists, researchers, and county agents initiated a survey to determine the prevalence of bacterial leaf scorch in Georgia's major blueberry production region, as well as whether or not resistance is present among some southern highbush cultivars. In late August, September, and October, county agents from major blueberry production counties helped to visually identify bacterial leaf scorch based upon symptoms. Samples were taken for confirmation through use of ELISA, and an estimate of disease incidence was collected for each site (% symptomatic plants). For each site, GPS coordinates were recorded to develop a map of the epidemic range.

Impact

Over time, this regional disease incidence map will serve as a baseline for epidemic observation of spread. Based on the results obtained, the nature of the epidemic may be better understood. The most valuable initial information derived from this survey is the determination of the degree of susceptibility of various cultivars. It does appear that resistance or tolerance does exist among some cultivars, and initial results show that FL 86-19, Star, and O'Neal are susceptible, with FL 86-19 being particularly susceptible; all three had a high incidence of infection. Windsor plants were confirmed to have the disease as well, but disease incidence was minimal (<1%). No Emerald, Millennia, or Southern Belle plants had any symptoms of disease. More detailed research will be needed to confirm this, but for now, the results are consistent across locations. These data provide good evidence that the solution to bacterial leaf scorch will likely involve genetic selection of resistant cultivars. If resistance is durable (lasting), then this will be important for the long-term health of the southern highbush industry. We still need to determine better ways of managing susceptible varieties, especially where they are already planted.

State Issue

Agricultural Profitability and Sustainability

Details

• Year: 2008
• Geographic Scope: Multi-County
• County: Appling
• Program Areas:
  • Agriculture & Natural Resources