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In vitro rescue and selection of spontaneous triploids by flow cytometry for easy peeler citrus breeding

Ollitrault P., Dambier D., Jacquemond C., Allent V., Luro F.. 1996. In : Proceedings International Society Citriculture. Volume 2. s.l. : s.n., p. 254-258. International Citrus Congress. 8, 1996-05-12/1996-05-17, Sun City (Afrique du Sud).

An improved method for obtaining triploid genotypes in one generation from diploid citrus has been developed. Clementine cultivars were pollinated with various cultivars of mandarins, sweet oranges, lemon and grapefruit. The abnormal and small seeds obtained from these crosses were germinated and cultivated in vitro. The ploidy level of the resultant plants was determined by flow cytometry and the triploid plants grafted onto C. volkamertana rootstocks. About 22 % of the plants obtained from in vitro rescue of small seeds were triploid. The cross with 'MA3' Clementine was most favourable for obtaining spontaneous triploids with a rate of 13 triploids per 100 pollinated flowers. With 'SRA 63' Clementine some male parents seem to be more efficient at inducing small seeds and triploids. Isozyme analysis was used to determine the origin of triploids. The data clearly indicated that diploid ovules do not result from diploid nucleus restitution from Clementine or the male parent but more probably from chromosome doubling of a haploid gamete. Considering the relative intensity of bands for heterozygous loci, it seems that the 2n gamete is of maternal origin. These results are in agreement with previous hypotheses of an origin of spontaneous triploids by fecundation of diploid ovules.

Mots-clés : citrus; citrus reticulata; citrus sinensis; citrus limon; citrus paradisi; triploïdie; méthode d'amélioration génétique; embryon végétal; corse; france; citrus deliciosa

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