LIBRO-CONGRESO-CITRUS

S14
stunting and low fruit yield and quality in some varieties regardless of the rootstock used. Characterization
of CTV isolates and estimation of their genetic variation can provide epidemiological information and be
useful for disease control. The first CTV outbreaks in Italy appeared in 2002: mild and severe isolates
in Sicily and mild isolates in the Apulia region (South-Eastern peninsular Italy). In this work, the genetic
variation of 12 mild and 18 severe CTV isolates from recent outbreaks occurred in the Calabria region
(South-Western peninsular Italy) was studied. Phylogenetic analysis of CTV p20 gene showed that the
Calabrian severe isolates clustered with severe isolates from other countries (including Egypt, Argentina
and India), whereas the Sicilian severe isolates were in other cluster together with severe isolates from
other countries (including Brazil, Spain, USA and China). This finding suggests distinct introductions for the
severe isolates from Calabria and Sicily. The nucleotide diversity was very low (0.002), suggesting a rapid
spread of CTV in Calabria. In another respect, the Calabrian mild isolates clustered with mild isolates from
California, Florida, Spain and Italy, some of them being identical to the Sicilian mild isolates and suggesting
that the Calabrian mild isolates could come from Sicily. Their very low nucleotide diversity (0.001) supports
also a rapid spread. However, the mild isolates from Apulia formed a subgroup with higher nucleotide
diversity (0.011) probably due to their earlier introduction.
S14P02
Incidence, distribution and first identification of Citrus tristeza virus by RT-PCR in citrus orchards
in South Western Nigeria
Adediji A.O. 1 , Atiri G.I. 1 , and Kumar P.L. 2
1 Department of Crop Protection and Environmental Biology (CPEB), University of Ibadan, Nigeria; and 2 Virology and Molecular
Diagnostics Unit (VMD), International Institute of Tropical Agriculture, Ibadan, Nigeria. adedapo.adediji@yahoo.com
In order to ascertain the presence, incidence, and distribution of Citrus tristeza virus (CTV), extensive
surveys were conducted in citrus growing areas of South-Western Nigeria during 2011-12. A total of 565
citrus trees were sampled in three states. Leaf samples from citrus trees were collected and symptom
severity was recorded. Symptoms observed included stem pitting, stunting, vein clearing and leaf curling.
Molecular analyses by RT-PCR of nucleic acid extracted from diseased samples were used to detect virus
presence using CTV-specific primers PIN1 and PIN2 directed to the conserved 3’ untranslated region.
Results show the presence of CTV in all the three states surveyed while symptom severity differed from one
location to another. Disease incidence varied from 85.2% in Oyo State to 48.4% in Ogun State. Citrus trees
were infected regardless of scion-rootstock combinations and were detected in sweet orange (87.0%),
tangerine (77.6%), grapefruit (73.8%) and lemon (69.5%). This is the first report of molecular detection of
CTV in Nigeria.
S14P03
A rapid procedure to evaluate the protecting ability of Citrus tristeza virus mild isolates against
severe isolates
Ruiz Ruiz S. 1 , Navarro-López J. 2 , Moreno P. 2 , and Ambrós S. 2
1 Instituto de Biología Molecular y Celular de Plantas (IBMCP), Valencia, Spain; and 2 Instituto Valenciano de Investigaciones Agrarias
(IVIA), Centro de Protección Vegetal y Biotecnología, Moncada, Valencia, Spain. suruirui@upvnet.upv.es
Measures to control damage caused by severe stem pitting isolates (SP) of Citrus tristeza virus (CTV) include
selective eradication and cross protection with mild strains (MS). Implementation of these measures needs
sensitive and specific methods to discriminate between SP and MS variants in the viral populations. We
developed a quantitative real-time RT-PCR method using TaqMan locked nucleic acid (LNA) probes that
enabled quantification of SP and MS variants in natural CTV populations. Here we used this method to
monitor the evolution of the CTV population in Pineapple sweet orange plants pre-inoculated with a MS
(T32) or a SP (T318) isolate, and then challenge-inoculated with budsticks infected with a SP or a MS
isolate, respectively. While control plants singly inoculated with T32 or T318 only contained the cognate
CTV variant in successive flushes, the plants doubly inoculated contained both types of sequence variants
in tissues derived from either the receptor plant or the inoculum budstick, with no strain impairing systemic
238 - VALENCIA CONFERENCE CENTER, 18th-23rd NOVEMBER 2012