Segregação Natural De Viróides Dos Citros Detectada Na Indexação Biológica E Bioquímica E Confirmada Pelos Sintomas De Plantas De Campo

Abstract

RESUMO -Estudaram-se os procedimentos de indexação biológica e bioquímica em um experimento de avaliação do uso de viróides como agentes ananicantes para pomeleiro 'Marsh Seedless'. Em algumas parcelas, houve segregação de viróides, sendo que, em duas, a segregação foi de CEVd (viróide da exocorte dos citros) e, em outras duas, não foi detectada a presença de CVd-II (viróide dos citros II). Como conseqüência desta segregação, não ocorreram sintomas típicos da exocorte em cidra nas parcelas nas quais houve segregação de CEVd, o que ocorreu nas parcelas em que a segregação foi de CVd-II, indicando que é necessária a presença de CEV para a manifestação de sintomas típicos de exocorte em cidra. Numa quinta parcela, não se detectaram viróides, provavelmente, devido à ausência dos mesmos no material de inoculação do teste biológico (escape), já que a planta de campo teve desenvolvimento vegetativo normal e ausência de sintomas no tronco. Finalmente, em uma sexta parcela, o que ocorreu, foi uma segregação drástica, não relatada na literatura, já que a planta de campo mostrou redução de porte e sintomas no tronco. A coleta de varetas para indexação deve ser mais rigorosa em função da ocorrência de segregação. Termos para indexação: cidra, exocorte, Citrus paradisi, pomelo, inoculação, Citrus medica SEGREGATION OF CITRUS VIROIDS DURING BIOLOGICAL AND BIOCHEMICAL INDEDEXINGABSTRACT -The procedures for biological and biochemical indexing were studied in an experiment to evaluate the use of viroids as dwarfing agents for 'Marsh Seedless' grapefruit. In some plots there was viroids segregation. In two plots the segregation was of CEVd (Citrus exocortis viroid) and in other two the presence of CVd-II (Citrus viroid II) was not detected. As a consequence of the segregation, there were no typical citron exocortis symptoms in the portions in which there was segregation of CEVd. Symptoms occurred in the portions, which there was the segregation was of CVd-II, indicating that the presence of CEV is necessary for the manifestation of typical symptoms of exocortis in citron. Viroids were not detected in a fifth plot, probably due to their absence in the inoculation material of the biological test (escapes), since the field plants showed normal vegetative development and absence of symptoms in the trunk. Finally, a drastic segregation, not referred to in the literature, occurred in a sixth plot, since the field plant showed canopy reduction and symptoms in the trunk. As a conclusion budwood sampling for viroid indexing must be more accurate.

Field performance of "marsh seedless" grapefruit on trifoliate orange inoculated with viroids in Brazil

“…Viroid segregation occurred in two plots on which trees received the CEVd isolate; in one of them there was a lack of CEVd in one tree, for the other the two trees had not CVd-II and in both plots reduction in tree size and scaling occurred (Stuchi et al, 2001). Such viroid segregation have also been reported in Israel (Hadas et al, 1989) and Australia (Broadbent et al, 1994 At the time of inoculation trunk diameters were similar to all treatments, indicating an uniformity of the experimental trees (Tables 1, 2).…”

“…The isolates were characterized by biological indexing and sPAGE (Stuchi et al, 1998) and the viroids had their complete genome sequenced (Targon et al, 2001) and registered in the GenBank under code numbers AF434678 (CEVd), AF434679 (HSVd, a non cachexia variant) and AF434680 (CVd-III). Inoculation was done in September, 1991, six months after planting, two buds per tree from trees carrying the isolates: one in the scion and the other one in the rootstock.…”