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Resumo -O objetivo deste trabalho foi obter plantas autotetraplóides de tangerina 'Ponkan', laranja 'Pêra-de-abril' e tangor 'Murcott', que serão usadas em cruzamentos com cultivares diplóides, visando à obtenção de indivíduos triplóides sem sementes. Utilizou-se o método de cultivo in vitro de segmentos de epicótilo em meio com colchicina (0,025, 0,05 e 0,1%), por diversos períodos (1, 2, 3, 7 e 14 dias), com subseqüente regeneração de brotações em meio sem a presença do alcalóide. As brotações foram microenxertadas in vitro e aclimatizadas em estufas. A determinação do nível de ploidia das plantas foi realizada por citometria de fluxo. A colchicina demonstrou ser tóxica aos explantes das três variedades, ocasionando redução significativa no número médio de brotações adventícias e aumento na porcentagem de explantes não-responsivos, em comparação com o controle. Entre as quatro plantas de laranja e uma de tangor obtidas, duas plantas de laranja e a de tangor, demonstraram ser autotetraplóides, apresentando folhas com maior espessura, arredondadas e coloração verde intensa. O método utilizado na duplicação cromossômica, com uso de colchicina, é eficiente em produzir plantas autotetraplóides de citros.Termos para indexação: Citrus, tetraplóide, epicótilo, regeneração in vitro, cultura de tecidos. Citrus autotetraploid plants obtained by in vitro treatment with colchicineAbstract -The objective of this work was to obtain autotetraploid plants of 'Murcott' tangor, 'Ponkan' mandarin and 'Pêra-de-abril' sweet orange to be used in crosses with diploid cultivars, aiming to produce triploid seedless hybrids. The methodology used was the in vitro culture of epicotyl segments in media containing different concentrations of colchicine (0.025, 0.05 and 0.1%), for several periods of time (1, 2, 3, 7 and 14 days), followed by the regeneration of adventitious shoots in culture media without the alkaloid. All shoots obtained were micrografted, acclimatized and transferred to a greenhouse. The evaluation of the ploidy level of the plants was performed by flow citometry technique. Colchicine was toxic to the explants of three varieties, and caused the reduction on the average number of shoots regenerated per explant as well as an increase in the percentage of non-responsive explants when comparing with the control plants. Among four plants of sweet orange obtained, two of them showed to be autotetraploid. The only plant of tangor obtained also showed to be autotetraploid. These plants presented thicker and roundisher leaves displaying deeper green color. The methodology used resulted efficient for obtaining tetraploid plants.

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In vitro tissue culture represents a useful technique for advancing Citrus breeding and propagation. Among in vitro regeneration systems, anther culture is commonly used to produce haploids and doubled haploids for a fast-track producing homozygous lines, in comparison with the traditional self-pollination approach, which involves several generations of selfing. In addition, anthers culture can produce somatic embryos that can also be used for clonal propagation. In this study, two thermal shocks were applied to the anthers of six Citrus genotypes (two clementine and four sweet oranges), just after they were put in culture. The response obtained was different depending on the genotype: both clementines, namely Hernandina and Corsica, produced homozygous and triploid regenerants (microspore-derived embryos), whereas all of the analyzed regenerants from sweet oranges, three cultivars of Tarocco and Moro, produced heterozygous and diploid regenerants similar to the parental genotypes (somatic embryos).