STUDIES ON THE CYTOTAXONOMY OF CITRUS Ⅰ. Karyotype and evolution of 30 taxa of the genera Citrus

The present paper deals with the karyotypes of 30 taxa of genus Citrus. The results obtained show that the chromosome numbers are 2ⁿ=18, belonging to small chromosome. All the karyotype consist of metacentric and submetacentric chromosomes with two to four satellite bodies born by the short arm. In addition, the heterozygosity in chromosomal length and arm ratio of some homologous chromosome were found in some taxa. The karyotypes belong to "2A" type of Stebbins's classification. The satellite chromosome of the species studied can be grouped into three types: large satellite (LS)-satellite much larger than short arm supported satellite; medium satellite(MS)-satellite and short arm close; Small satellite(SS)-satellite small, short arm large. Furthmore, the variation in the number and size of satellite can be used as a stable genetic marker in studing Citrus biosystematics. From karyotypical analyses, author support that C.grandis is one of the three basic species, while C.reticulata should be studied in various wild mandarins further, and suggest that C.limonia, C.paradisi, C.sinensis, C.aurantium, C.wilsonii, C.sulcata and in part of C.reticulata have hybrid origin. The evolution of karyotype from asymmetry to symmetry is correlated with the trend of evolution of the morphological characters and pollen morphology.