|Bergamin Filho, A.|
Submitted to: Plant Disease Epidemiology International Workshop
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2005
Publication Date: 6/1/2005
Citation: Laranjeira, F.F., Bergamin-Filho, A., Amorim, L., Gottwald, T.R., Berger, R.D., Lopes, J.R.S. 2005. Spatial-temporal dynamics of citrus variegated chlorosis in Sao Paulo State, Brazil. Proceedings of the 9th International Workshop on Plant Disease Epidemiology. C8 p. 55. Interpretive Summary:
Technical Abstract: Citrus variegated chlorosis (CVC) is one of the most important citrus diseases in Brazil. It is caused by Xylella fastidiosa, a xylem-limited bacterium transmitted by sharpshooter leafhoppers (cicadellids). CVC is widespread in most brazilian citrus areas but incidence and severity can be quite different. In Sao Paulo state there's an incidence gradient between regions and some hypothesis were created to explain it. This study aimed to point out differences and similarities between Northwest, Center and South regions of Sao Paulo concerning CVC progress and spread, and also describe and find relationships between seasonal patterns of vectors, host growth, pathogen and disease. Three areas ('Pera' sweet orange grafted on Rangpur lime), one in each region, were evaluated for two years by visual assessments performed two times a month. For each evaluation all plants were inspected, assigned as diseased or healthy and cumulative maps were produced. Nine models were fit to each CVC progress curve, and three were fit to segments of original curves. Also, first and second derivatives were estimated for each curve. The following spatial analyses were performed: ordinary runs, isopath areas, Taylor law, dispersion index and foci structure and dynamics analysis. In order to establish differences in seasonal pattern of pathogen, vectors, host and disease, 20 symptomatic plants in each orchard were monthly evaluated. The following variables were measured: number of new flushes (nf), percentage of symptomatic branches (psb), percentage of infected asymptomatic branches (piab), percentage of infected branches (pib), estimation of bacteria concentration (ebc), lower and higher temperatures, rain fall and number of sharpshooters in yellow traps. The correlations among variables were tested by Distributed Lag Analysis, and the comparison between regions and seasons was performed by Kruskal-Wallis, Friedman ANOVA and Nemenyi test (p<0,005). Temporal. Good fitting was obtained for segments of original curves. First and second derivatives showed many peaks over time. Most of those peaks occurred at spring and summer months. Our hypothesis is that derivative peaks are related to flush emission peaks, considering that new sprouts are the preferred feed site of Xylella fastidiosa vectors. Spatial. Ordinary runs indicated a trend to randomness. lsopath areas analysis showed few compact foci and a trend to uniform incidence in all areas. The other analysis showed few if any differences between regions and results that could classify CVC pattern as slightly aggregated. Seasonal patterns. The CVC related variables (psb, piab, pib and ebc) showed seasonal patterns but no statistical differences were detected among seasons. The Northeast orchard showed the highest number of new flushes and percentage of symptomatic branches. The South orchard had the higher percentage of asymptomatic infected branches. There were no statistical differences among regions concerning Xylella concentration.