LIBRO-CONGRESO-CITRUS

S14O01
Recent developments on Citrus tristeza virus research
Folimonova S.
University of Florida, Citrus Research and Education center, Plant Pathology, USA. svetlana@ufl.edu
Citrus tristeza virus (CTV) causes two citrus diseases that cause economic losses in citrus production globally:
quick decline on sour orange rootstocks and stem pitting. Recent research results from several labs around
the world provided valuable contributions that greatly increase our understanding of the virus-citrus host
interactions as well as generate a necessary foundation for development of effective procedures to manage
CTV diseases. Our lab demonstrated that p33, p13, and p18 proteins are required for systemic infection of some
citrus varieties, suggesting that genes of these nonconserved proteins were acquired during virus evolution to
extend its host range. Another interesting discovery was demonstration that stem pitting does not necessarily
result from a specific sequence or protein, but from a balance between the expression levels of different viral
genes. Several important results were obtained by IVIA researchers in Valencia, Spain. One of them was the
development of a long-awaited successful strategy for obtaining transgenic resistance against CTV by expression
of untranslatable versions of genes encoding the three silencing suppressors of CTV, p25, p20, and p23. Crossprotection
has been an effective management procedure that has allowed economic production of citrus in
some regions in which endemic severe isolates of CTV made citrus production unprofitable. However, finding
protecting isolates has been empirical and rarely successful. Research results obtained by our lab has advanced
our understanding of how CTV cross-protection works, showing that exclusion works only for isolates within
a strain, and, thus, provided a “recipe” for selection of protective isolates. A next frontier of virus biology is
developing an understanding of how viral populations form, induce symptoms, and react to cross protect. Some
progress in this area has been done. These and other recent contributions will be discussed.
S14O02
Large scale survey of Citrus tristeza virus (CTV) and its aphid vectors in Morocco
Afechtal M. 1 , Djelouah K. 2 , Cocuzza G. 3 , and D’Onghia A.M. 2
1 National Institute of Agricultural Research (INRA), Plant Protection, Morocco; 2 Mediterranean Agronomic Institute (IAMB), Integrated
Pest Management of Mediterranean Fruit Crops, Italy; and 3 University of Catania (UNICT), Science and Phytosanitary Technologies,
Italy. mohamedafechtal.inra@gmail.com
A survey of Citrus tristeza virus (CTV) was carried out in the main Moroccan citrus growing areas (Souss, Gharb,
Moulouya, Tadla, Haouz, Loukkos). A total of 3,208 plants from commercial groves, nurseries, plots of budwood
sources and varietal collections were analyzed by DTBIA. About 26% of the tested trees proved to be CTVinfected
in the groves, mainly in Loukkos region with a 60% infection rate. On the contrary, just a few infected
trees were detected in Souss and Gharb regions. No CTV infections were found in the remaining investigated
sites. CTV vectors were monitored in Gharb and Loukkos regions. Aphis spiraecola (56%) and A. gossypii (33%)
were the most abundant aphid species, while no evidence of Toxoptera citricidus was reported. Four out of six
selected Moroccan CTV isolates showed, by coat protein gene sequencing, the highest nucleotide homology
with the Spanish mild isolate T385. The remaining isolates, from Loukkos, clustered close to the Portuguese
19-21 reference strain; one of these induced a mild stem pitting on Duncan grapefruit by biological indexing.
This study confirmed CTV genetic diversity in some Moroccan orchards. The finding of the stem pitting form
represents a serious threat to the Moroccan citrus industry, mainly if T. citricidus is introduced in the country.
S14O03
Capillary electrophoresis-single–strand conformation polymorphism and multiple molecular
marker genotyping allow a rapid differentiation of CTV isolates
Licciardello G. 1 , Russo M. 1 , Daden M. 2 , Bar-Joseph M. 3 , and Catara A. 1
1 Parco Scientifico e Tecnologico della Sicilia (PSTS), Italia; 2 International Plant Analysis and Diagnostics S.r.l. (IPADLAB), Italia; and
3 GimlaoTec, Israel. acatara@pstsicilia.it
Despite the noticeable sensitivity to Citrus tristeza virus (CTV), the sour orange rootstock remains popular in
some Mediterranean areas because of its horticultural advantages. Since some trees remain symptomless,
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