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Citrus Sudden Death Is Transmitted by Graft-Inoculation and Natural Transmission Is Prevented by Individual Insect-Proof Cages

February 2011 , Volume 95 , Number  2
Pages  104 - 112

Pedro T. Yamamoto, Renato B. Bassanezi, Nelson A. Wulff, Mateus A. Santos, André L. Sanches, Rodrigo S. Toloy, Nelson Gimenes-Fernandes, and Antonio J. Ayres, Departamento Científico, Fundo de Defesa da Citricultura, Fundecitrus, Av. Dr. Adhemar Pereira de Barros, 201, CEP 14807-040, Araraquara – SP, Brazil; Waldir C. Jesus Junior, Laboratório de Fitopatologia, Departamento de Fitotecnia, Universidade Federal do Espírito Santo, Alto Universitário, S/N, CEP 29500-000, Alegre – ES, Brazil; Tatsuya Nagata, Departamento de Biologia Celular, IB4, Universidade de Brasília, ICC Ala Sul, Asa Norte, CEP 70910-900, Brasília – DF, Brazil; Francisco A. O. Tanaka and Elliot W. Kitajima, NAP/MEPA, Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo, Av. Pádua Dias, 11, CEP 13418-900, Piracicaba – SP, Brazil; and Joseph M. Bové, Unité Mixte de Recherche en Génomique, Développement et Pouvoir Pathogène, Centre de Recherche INRA de Bordeaux, 71, Ave. Edouard Bourlaux, 33883 Villenave d'Ornon Cedex, France



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Accepted for publication 31 August 2010.
Abstract

Citrus sudden death (CSD) transmission was studied by graft-inoculation and under natural conditions. Young sweet orange trees on Rangpur rootstock were used as indicator plants. They were examined regularly for one or two characteristic markers of CSD: (i) presence of a yellow-stained layer of thickened bark on the Rangpur rootstock, and (ii) infection with the CSD-associated marafivirus. Based on these two markers, transmission of CSD was obtained, not only when budwood for graft-inoculation was taken from symptomatic, sweet orange trees on Rangpur, but also when the budwood sources were asymptomatic sweet orange trees on Cleopatra mandarin, indicating that the latter trees are symptomless carriers of the CSD agent. For natural transmission, 80 young indicator plants were planted within a citrus plot severely affected by CSD. Individual insect-proof cages were built around 40 indicator plants, and the other 40 indicator plants remained uncaged. Only two of the 40 caged indicator plants were affected by CSD, whereas 17 uncaged indicator plants showed CSD symptoms and were infected with the marafivirus. An additional 12 uncaged indicator plants became severely affected with citrus variegated chlorosis and were removed. These results strongly suggest that under natural conditions, CSD is transmitted by an aerial vector, such as an insect, and that the cages protected the trees against infection by the vector.



© 2011 The American Phytopathological Society