Severity and genetic diversity of Citrus tristeza virus complexes infecting ‘Pêra Bianchi’ sweet orange in Paraná, Brazil

Abstract

The aggressiveness and genetic diversity of the Citrus tristeza virus (CTV) infecting sweet orange ‘Pera Bianchi’ (Citrus sinensis) trees were evaluated under the environmental conditions of the state of Parana, 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 Paranavai 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 ‘Pera 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 Parana.