LIBRO-CONGRESO-CITRUS

S14P08
Population variation of Citrus tristeza virus
Qing L. 1 , Ruan T. 1 , Xiong Y. 1 , Zhou Y. 2 , Song Z. 2 , Sun X.C. 1 , Li Z.A. 2 , and Zhou C.Y. 2
1 Southwest University (SWU), College of Plant Protection, China; and 2 Chinese Academy of Agricultural Sciences (CAAS), Citrus
Research Institute, China. qling@swu.edu.cn
Using the specific primer pair P23f (5’-TAAGAGTCTGCGAGTTACGATG-3’) and P23r (5’-TCCGTCCACTTCAATCAG-3’),
the p23 gene of severe (CT3 and CT14) and mild (CT11 and CT18) isolates of Citrus tristeza virus (CTV) from
grapefruit (CT3 and CT18) and sweet orange (CT11 and CT14) were amplified by RT-PCR and cloned. Eighty
six clones of this gene were chosen randomly for sequencing, which composed four CTV populations.
Genetic structure and variability of these populations were analyzed. The results demonstrated that all CTV
populations were heterogeneous, consisting of sequences that were not identical but closely related to the
consensus sequence. The percentage of mutated clones (41.7%) and mutation frequency (8.8×10-4) of the
CT11 population were highest among these four populations, whereas those of the CT3 population, with
only 13.0% percent of mutated clones and 2.0×10-4 mutation frequency were lowest. The CT14 and CT18
populations shared the same mutation frequency (5.0×10-4), but the percentage of mutated clones of CT14
(26.7%) was lower than that of CT18 (33.3%). Comparison of the variability of CTV mild isolates in different
hosts showed that the percentage of mutated clones and mutation frequency of CT18 from grapefruit were
lower than those of CT11 from sweet orange. Similarly, the percentage of mutated clones and the mutation
frequency of the severe isolate CT3 from grapefruit were lower than that of CT14 from sweet orange,
suggesting that variability of CTV is higher in sweet orange than in grapefruit. The consensus nucleotide
sequence of CT3 has the highest identity (97%) with CT18 and the lowest (89.7%) with CT14, whereas highest
identity of CT11 (95.5%) is with CT14 and the lowest (91.4%) with CT18. Substitution and deletion mutations
were detected in CTV populations with the dominant mutation type being base transition from G to A.
S14P09
Nucleotide sequence of three genes of Citrus tristeza virus from selected isolates in a program of
preimmunization.
Zanutto C.A., Müller G.W., Corazza M.J., and Nunes W.M.C.
Universidade Estadual de Maringa (UEM), Nucleo de Pesquisa em Biotecnologia Aplicada, Brazil. william.nunes@pq.cnpq.br
Two capsid proteins (p25 and p27) are required for the correct assembly of Citrus tristeza virus (CTV) virions
and for cell-to-cell movement. Protein p25 is also a suppressor of post-transcriptional gene silencing, as also
is the p23 protein. To further advance in the knowledge on CTV isolates present in the Paraná State, Brazil,
variability of the p23, p25 and p27 genes of two CTV isolates was analyzed. The isolates chosen for this study
were the mild isolate CS-1, selected as protecting isolate for preimmunization in the Paraná State, Brazil,
and the severe isolate called Rolândia, that has caused severe symptoms in many orchards in the North of
the State and has been used as control in this program. The p23, p25 and p27 products RT-PCR amplified
from these isolates were cloned, and multiple clones for each gene and isolate were sequenced. From the
Rolândia isolate, five haplotypes were obtained for the p23 gene, five for the p27 and seven for the p25 (out
of 10 clones), which showed identity values ranging from 82.5 to 97.5%, 95.1 to 98 3% and 92.3% to 99.2%,
respectively. From the CS-1 mild isolate four haplotypes of the p25 gene and three haplotypes of the p27 gene
were obtained, which showed identity values ranging from 96.2 to 99.3% and 98.3 to 99.1%, respectively.
S14P10
A comparative study and vector transmissibility of relevant Citrus tristeza virus (CTV) populations
from Italy indicates a risk for further epidemics
Yahiaoui D. 1 , Djelouah K. 1 , D’Onghia A.M. 1 , and Catara A. 2
1 CIHEAM-Mediterranean Agronomique Institute of Bari (CIHEAM-MAIB), Integrated Pest Management, Italy; and 2 Università degli
Studi di Catania, Dipartimento di Science e Tecnologie Fitosanitarie (DISTEF), Italy. djelouah@iamb.it
In Italy, Tristeza declining trees on sour orange rootstock trace back to 2002. A mild and a seedling yellows
Citrus tristeza virus (CTV) population were the causes of heavy losses on Navelina and Tarocco sweet oranges
XII INTERNATIONAL CITRUS CONGRESS 2012 - 241
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