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Analise citogenetica em tres cultivares de laranja doce (Citrus sinensis (L.) Osbeck) (Cytogenetical investigations of three cultivars of sweet oranges (Citrus sinensis (L.) Osbeck)

Yone M. Sellito-Boaventura^I; Rose Mary Pio^II

^ISeção de Citologia
^IISeção de Citricultura, Instituto Agronômico, Caixa Postal 28, 13020 Campinas; SP., Brasil. Enviar correspondência para Y.M.S.B

ABSTRACT

Three cultivars of sweet oranges of precocious to mid-season maturation, `Pineapple', `Ruby' and `Moro', were selected among 18 thus far characterized in the germplasm bank of the Instituto Agronômico as having a different average number of seeds per fruit. To determine the possible reasons for this difference in number of seeds, wé studied microsporogenesis, which permitted the determination of chromosome number and analysis of meiotic behavior.
The chromosome number of the three cultivars was n = 9 and at diakinesis there was formation of 9<sub>II.</sub> At first metaphase, `Pineapple' showed 18 chromosome for all cells, while `Ruby' and `Moro' showed 19 chromosomes in 6.0% and 9.0% of the cells, respectively. At first anaphase, 94.0% of the cells of `Pineapple' exhibited normal segregations to the poles, while at second anaphase the frequency was 84.5%.
Irregular segregation to the poles and some "laggards" were observed at first and second anaphases in `Ruby' and `Moro'.
The percentage of normal tetrads and viable pollen were 75.2% and 64.4% for `Pineapple', 59.8% and 33.0% for `Ruby', and 56.4% and 2.4% for `Moro', respectively.
Pineapple' showed more regular meiotic behavior than the other two cultivars. Meiotic behavior was particularly irregular in `Moro', probably explaining the lower production of seeds of this cultivar.

Keywords: cytogenetical; investigations; oranges; Citrus sinensis.

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