Spatial dynamics of citrus variegated chlorosis (CVC) foci by symptoms and serology

Abstract

Relationship between incidence of citrus variegated chlorosis (CVC) and causal agent Xylella fastidiosa was determined by symptoms and serology (DIBA - Dot Immunobinding Assay) for foci analysis. Experimental area consisted of an orchard of sweet orange ‘pêra’, Citrus sinensis (L.) Osbeck, grafted on Rungpur lime (Citrus limonia Osbeck) (Rutaceae). Experimental area consisted of two blocks, with 15 rows and 10 plants/row, with a total of 300 plants. Four evaluations were made and all plants in the four quadrants of each block were evaluated for symptoms. Twenty leaves of each plant were collected for serological analysis. In the first evaluation, the number of foci for symptoms was smaller than that obtained by DIBA. In the second, third and fourth evaluations the number of foci for symptoms was 3.1, 4.1 and 4.5 times higher than that obtained by DIBA. On the other hand, foci defined by DIBA were always larger than the ones defined for symptoms. Ninety per cent of foci evaluated by symptoms and seventy per cent evaluated by DIBA were smaller than 10 plants. Averages of compact foci index (CFI) were practically similar: 0.86 for the evaluation for symptoms and 0.85 for DIBA. The average of the form foci index (FFI) was 1.17 by symptoms and 0.94 by DIBA. Highest efficiency of detection of incidence for DIBA in relation to symptoms is checked by the smallest number of foci and unitary foci, as well as for the largest number of plants per foci. The importance of more sensitive methods to study the CVC epidemiology is thus enhanced