Comparison of Citrus tristeza virus (CTV) isolates by RFLP analysis of the coat protein nucleotide sequences and by the severity of the symptoms

Abstract

Plants of Pera sweet orange on Rangpur lime rootstocks, from orchards of the northwest and north of Paraná state, Brazil, were evaluated for severity of symptoms and genetic diversity of Citrus tristeza virus. The severity of symptoms was evaluated by the development of tree, fruit size and stem pitting symptoms. Isolates that infect these plants were compared with known mild and severe isolates by analysis of restriction fragments length polymorphism (RFLP) of the coat protein nucleotide sequences (CPNS), amplified by the polymerase chain reaction (PCR) and undergone digestion with the restriction enzymes Hinf I and Rsa I. The severity of symptoms showed that the analyzed plants from the northwest orchards presented mild to moderate tristeza symptoms, while the plants from the north orchards exhibited moderate to severe symptoms. The RFLP analysis revealed that the CTV isolates are constituted by haplotype mixtures. Rsa I was the enzyme that best discriminated the genetic diversity among the analyzed isolates of CTV. Two main groups were generated by the UPGMA analysis. The isolates from the northwest orchards grouped with most of the mild isolates used as control, and a great part of the isolates from the north orchards, was correlated with the severe isolate Capão Bonito. Correlation between the stem pitting intensity and RFLP patterns, was demonstrated with some exceptions. The failure of protection of some isolates and the contamination of the rootstocks by the severe isolates, in field nursery conditions, before grafting with scions with mild isolates, were the hypotheses considered to explain the occurrence of severe CTV isolates in the North area of Paraná State.

Agronomic performance of Pera and related sweet orange accessions naturally infected with Citrus tristeza virus in northern Paraná State, Brazil

“…In the State of Paraná, Brazil, changes have been identified in the CTV protective complex in use and also the presence of severe strains of the virus in different accessions of Pera sweet orange (Carraro et al, 2003;Costa et al, 2010;Corazza et al, 2012;Zanutto et al, 2013). Therefore, accessions of cross-protected mother trees introduced from other regions of Brazil or naturally infected selected trees may not perform well in the presence of the citrus tristeza disease in Paraná (Corazza et al, 2012;Zanutto et al, 2013).…”

“…Therefore, accessions of cross-protected mother trees introduced from other regions of Brazil or naturally infected selected trees may not perform well in the presence of the citrus tristeza disease in Paraná (Corazza et al, 2012;Zanutto et al, 2013).…”

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

“…The threats result from the endemic presence of the virus, the high transmission efficiency of the virus by the vector Toxoptera citricida (Souza and Müller 2006), and the use of one single mild isolate in the preimmunization programs (Müller et al 1999). For instance, changes in the cross-protective CTV isolates have been detected in the state of Paraná (Carraro et al 2003;Costa et al 2010;Corazza et al 2012;Zanutto et al 2013).…”

The effect of drought conditions on sweet orange (Citrus sinensis) plants infected with citrus tristeza virus (CTV)

“…The choice of scion variety, rootstock and seedlings to be planted is a decisive factor in planting trees in an orchard that will be tolerant or prevent colonization by the virus (Silva and Souza 2002;Bastos et al 2014). According to Corazza et al (2012), if rootstocks in the field are alraedy colonized with severe CTV isolates before being grafted and inoculated with mild isolates, the severe isolates will predominate in the area in question. Rangpur lime (Citrus limonia Osbeck) is the most commonly used rootstock in citriculture in Brazil due to its tolerance to CTV and its adaptation to water deficiency.…”