|Verniere, C. J.|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2003
Publication Date: 7/1/2003
Citation: Verniere, C. J., Gottwald, T. R., Pruvost, O. 2003. Disease Development and Symptom Expression of Xanthomonas Axonopodis pv. citri in Various Citrus Plant Tissues. Phytopathology 93:832-843 Interpretive Summary: Citrus canker is one of the most serious diseases of citrus worldwide due to the damage it causes and the affect on local, national and international commerce due to quarantines and embargos. When the disease becomes permanently established and eradication is not an option, then disease management strategies must be considered. Reunion Island in the Indian Ocean is such a place an offered a unique opportunity to examine disease management of citrus canker. This study deals with the examination of various environmental factors and their interaction and affect on disease expression. These affects were examined on infection of leaves, stems and fruit for different cultivars of citrus and various ages of tissues. Following a complex analyses aimed at determining those factors with the greatest influence and their interactions, complex models were developed to predict the amount of disease that will occur as a result. The information and models generated in this program will be used to better manage the disease in Reunion and perhaps other areas where citrus canker exists and must be managed.
Technical Abstract: Experimental inoculations of Xanthomonas axonopodis pv. citri (Xac) in different tissues of Tahiti lime and Pineapple sweet orange were conducted monthly under natural conditions in Réunion Island. The interactions between a set of environmental and epidemic variables associated with disease expression and 184 different factor combinations were investigated in order to determine the parameters needed to explain ACC disease expression. Area under the disease progress curve (AUDPC), and inoculation date (Id), Fruit and Leaf Age Ratings (FAR and LAR), and number of days during the first two weeks post inoculation for which the temperature was less than 14°C (Tmin) or more than 28°C (Tmax) were retained by Principal Component Analysis and canonical correlation analysis as the most meaningful epidemic and environmental variables respectively. AUDPC as the strongest dependent variable and combinations of the environmental variables, as independent variables, were used in multiple regression analyses. Tissue age rating at the time of infection was a good predictor for disease resulting from spray inoculation on fruits and leaves and also on fruits following a wound inoculation. Temperature, as expressed by Tmin or Tmax, was also a significant factor in determining disease development described by AUDPC. Mature green stems were highly susceptible after wounding similarly to leaves but buds and leaf scars expressed the lowest susceptibility. These variations in disease expression according to the tissues will have different impacts on ACC epidemiology.