|Graham, James - UNIV. OF FLORIDA|
|Schubert, Tim - FL DEPT. OF AGR.|
Submitted to: Society of Citrus Nurserymen International Congress
Publication Type: Proceedings
Publication Acceptance Date: March 24, 1997
Publication Date: N/A
Interpretive Summary: The increase and spread of Asiatic citrus canker, caused by a plant pathogenic bacterium, in the Miami area was studied in respect to its interaction with the newly introduced Asian leaf miner, human movement, and weather events including rainstorms, tropical storms, and hurricanes that have occurred in the area in the last 3 to 4 years. The Asian leaf miner was found to exacerbate the citrus canker epidemic manyfold by causing numerous new canker infections. Human movement of potted plants and fruit contributed to short distance movement of the bacteria. The major contributor to spread was determined to be rainstorms associated with tropical storms and hurricanes. Two such storms were correlated with major citrus canker spread events. The disease was found to be expanding predominately in the northeast direction. A spread of up to seven miles was measured from a single storm event. In addition, the epidemic was backtracked to possible sources. Although the original introduction was not found, the area where the most probable introduction occurred was identified. Although no commercial citrus areas are yet involved, the potential for long distance spread combined with rapid inoculum build up due to the interaction with the leaf miner, places commercial citrus at future risk. These analyses are used to determine the most probable areas of disease expansion to direct eradication efforts.
Technical Abstract: Asiatic citrus canker caused by Xanthomonas axonopodus pv citri (Xac) was discovered in residential citrus in Miami, Florida, in September 1995. Genetic analyses indicated that Miami isolates of Xac differ from isolates collected during earlier outbreaks in 1986-1992 and represent a unique introduction. The infested area has increased from 14 to 86 sq. mi. despite efforts to eliminate infected trees. Inadvertent human transport resulted in predominantly local, short distance spread. In contrast, thunderstorms, tropical storms, etc. with blowing winds and rain, have contributed to medium to long distance dispersal of Xac from the original focus. Disease gradients examined in October 1995, appeared to emanate from an area 1.5 miles southeast of the Miami International Airport, implicating spread by storms. In the putative focus area, the oldest stem lesions document the existence of citrus canker in the area for at least 2 to 3 years. The age of infections in newly infested areas correspond well with recent, tropical storms that have resulted in the subsequent spread of Xac to the northeast. Extensive lesion development on leaves damaged by leaf miner provided for rapid build-up of inoculum, which when combined with storm events and leafminer interaction has resulted in an exacerbation of disease and rapid epidemic development.