Haploids Obtained from Diploid*Triploid Crosses of Citrus.

Abstract

Four monoembryonic diploid (2n = 18) citrus cultivars and hybrids were crossed with a triploid (2n = 27) hybrid derived from a cross between diploid Citrus medioglobosa X tetraploid C. funadoko and C. natsudaidai cv. Kawano. Seeds were collected from all fruits of all crosses at maturity, and fully developed seeds were germinated. The seedlings produced exhibited several ploidy levels. While most were diploid, some were haploid, aneuploid, triploid or tetraploid. Haploidy was observed in 2 seedlings out of 116 in the cross involving Clementine and 1 out of 54 in the cross involving Lee. There was no difference in size between haploid and diploid embryos. Haploid embryos germinated normally and their primary roots elongated vigorously. Haploid plants transplanted to soil, however, grew very weakly. Restriction endonuclease analyses of nuclear ribosomal DNA and of ctDNA were performed to determine the origin of the haploids. The 3 haploid plants had rDNA and ctDNA fragments specific to the seed parent, but no fragments specific to the pollen parent. This finding indicates that the haploids were of maternal origin