Analysis of 45S rDNA Loci of Natural Tetraploid and Corresponding Diploid in Citrus by FISH

摘要

Aiming to study the origin of natural tetraploids from citrus seedlings, three diploid female Font parents of different embryony number types (monoembryony, polyembryony, the mixture monoembryony and polyembryony) and their natural tetraploid progenies were used for 45S rDNA loci analysis by FISH (Fluorescence in situ hybridization). Diploid female parents were C. limon (' Femminello'), C. grandis (' Shatianyou')and C. sinensis (' Hongjiangcheng'). The number of 45 S rDNA loci of the diploid and tetraploid of ' Femminello' was three and four respectively. Three 45S rDNA loci of diploid were detected all on centromeric region, while two loci of tetraploid located on telomeric region of short arm and other two were on centromeric region, which indicated that formation of natural tetraploids of ' Femminello' should be relative to sexual hybridization with foreign genome. The diploid of 'Shatianyou' had four 45S rDNA sites, and natural tetraploids of 'Shatianyou' had eight or six sites. The signal location and intensity of tetraploids of ' Shatianyou' were complicated in different individuals. These signal information suggested that these tetraploids were possibly autotetraploid or allotetraploid. The number of 45S rDNA sites of diploid of ' Hongjiangcheng' was three, and its tetraploid had six sites. According to similar signal character, tetraploids of 'Hongjiangcheng' should be from chromosome doubling of nucellar cells. In conclusion, natural citrus tetraploids could be from sexual hybridization with recombination of foreign genome when female is a monoembryony or the mixture of monoembryony and polyembryony. While female parent is polyembryonic, natural tetraploids maybe come from chromosome doubling of nucellar cells.