Disseminação da Clorose Variegada dos Citros (CVC) no Recôncavo Baiano: disponibilidade de inóculo em plantios e material propagativo

Abstract

Bahia ranks second in the production of Brazilian citrus fruits, but Citrus Variegated Chlorosis (CVC), a major citrus disease, is present in the state. The causal agent is Xylella fastidiosa subsp. pauca a xylem-limited bacterium. Despite some information about CVC in the Litoral Norte region of Bahia, there are no comparative epidemiological studies for the Reconcavo region in Bahia. The aim of this study was to characterize the dynamics of CVC in citrus orchards and quantify the spread risk associated with propagating material in the Reconcavo. Two orchards of Pera sweet orange grafted on Rangpur Lime were selected. The percentage of symptomatic branches, the percentage of infected branches (Asymptomatic + Symptomatic), and the number of new shoots. The greatest expression of symptoms occurred from May to October, which coincided with the largest number of shoots. There was no increasing trend in the incidence of infected branches, which had three-month cycles throughout the year. These cycles may be related to the climatic conditions of the region. There was inoculum and host biomass availability throughout the year. To determine the spatial dynamics of CVC, the plants in the selected areas were visually evaluated and mapped every month. The spatial pattern was determined by calculating the dispersion index (DI) and applying the modified Taylor's law. The DI for most evaluations showed values higher than 1 (X2, P<0,05), indicating a spatial dependency between plants within quadrats. Similar results were observed when Taylor‟s law was applied for all quadrats sizes. CVC spatial pattern showed no significant differences between the evaluated areas, indicating in both cases a tendency to aggregation. These results do not differ from the patterns observed for the same disease in other regions of Brazil. To assess the risk of dispersion associated with propagation material, a total of 190 samples of different varieties were collected in the germplasm bank of Embrapa Cassava and Fruits and analyzed by qPCR. All samples were negative for the presence of the CVC pathogen.