Brazil is one of the world's largest producers of citrus. However, production is challenged due to biotic and abiotic factors limiting crop health. The aim of this work was to evaluate the influence of water deficit in sweet orange (Citrus sinensis) cv. Pera Bianchi inoculated with citrus tristeza virus (CTV). Two isolates of CTV were used, one causing severe symptoms (Forte Rolândia) and the second causing mild symptoms (Pêra IAC), grafted on Rangpur lime (Citrus limonia) and Swingle citrumelo [Citrus paradisi x Poncirus trifoliata], and the indicator sweet orange Pêra Bianchi, free of virus, and healthy controls containing only the indicator budwood. The water regime for the plants was field capacity or 50% field capacity. After five months of controlled irrigation, biochemical variables were measured (protein, proline content and catalase activity), and real-time RT-PCR amplification of the virus was performed for detection and quantification of viral titer. Differences were observed in the total protein content and proline, with greater accumulation in plants maintained under water deficit. There was no effect of drought on the population of viral isolates, but the plants held at field capacity and inoculated with the severe isolate had a higher viral titer.

The aggressiveness and genetic diversity of the Citrus tristeza virus (CTV) infecting sweet orange 'Pêra Bianchi' (Citrus sinensis) trees were evaluated under the environmental conditions of the state of Paraná, Brazil. Disease severity was assessed based on stem pitting symptoms in the citrus trees, while genetic diversity was determined by sequencing the virus coat protein (CP) gene. Stem pitting symptoms were less severe in trees maintained under greenhouse conditions and field experimental plots in the municipalities of Paranavaí and Umuarama, where the temperature is higher. In contrast, the most severe stem pitting symptoms were observed in trees from experimental orchards established in colder areas (i.e. municipalities of Arapongas, Cascavel and Londrina), suggesting a temperature effect on symptom development. Analysis of CP sequences indicated intra-and interspecific diversity of the CTV complex for most of the trees included in this study. Recombination analyses of the CP gene also allowed to identify recombinants with parentals related to PIAC-5, a mild isolate, and 1BL-3, found in trees from a field plot in Londrina. The CTV complex infecting 'Pêra Bianchi' trees under field conditions showed a high degree of genetic diversity, implying the possibility of multiple infections or even a dynamic rearrangement of the genotypes into different CTV complexes under the environmental conditions of the state of Paraná.