No abstract

Despite of the susceptibility to the Citrus tristeza virus (CTV), Pera sweet orange is the most important citrus cultivar in Brazil. The objective of this study was to evaluate the CTV aggressiveness and the relationship with the agronomic performance of 24 accessions of Pera and related sweet oranges. Accessions belonging to the Citrus Germplasm Collection of the Instituto Agronômico do Paraná (IAPAR), Londrina, PR, were included in the study. Citrus tristeza disease was rated based on the severity of stem pitting symptoms. Yields were evaluated in the 2010/2011, 2011/2012, and 2012/2013 seasons, and tree growth in 2012. The best performance regarding stem pitting severity was shown by Redonda accession, followed by Ipiguá II. Vegetative tree vigor was more evident for Redonda, Tardia CO3, and Guilherme Spagnol accessions. These Pera and related sweet oranges accessions also showed the highest fruit yields, along with Vimusa, Santa Tereza, Ipiguá, Ipiguá II, D-6, and Paulo Rosa. Vegetative tree vigor, yield and number of fruits were inversely correlated with citrus tristeza disease stem pitting severity. Therefore, the poor agronomic performance of some Pera and related sweet oranges is probably related to the presence of severe CTV complexes infecting these accessions.

‘Pêra’ sweet orange is the most important citrus cultivar in Brazil, but it is highly susceptible to Citrus tristeza virus (CTV), the causal agent of citrus tristeza disease. In this study, we evaluated the severity of citrus tristeza disease and its relation with the agronomic performance of seven cultivars and six selections of ‘Pêra’ sweet orange under field conditions in the North and Northwest regions of the State of Paraná, Brazil. The citrus tristeza disease severity was determined based on symptoms of stem pitting. The vegetative growth assessed in trees of all four locations for the 2012 season, and in two field plots for the 2011, 2012 and 2013 harvests, respectively. The cultivar ‘IPR 153’ (Bianchi) had the best performance concerning stem pitting severity, while Selection 27 was among the ones with the highest rate of vegetative growth. Further, Selections 27 and 12, and the cultivar ‘Vimusa’ had the largest fruit yields. Based on correlation analysis, stem pitting symptoms severity was negatively correlated with vegetative growth and fruit yield. Furthermore, environmental conditions may have played an important role in the severity of citrus tristeza disease and consequently on the agronomic performance of the cultivars and selections of ‘Pêra’ sweet orange in the North and Northwest regions of the State of Paraná.

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.