Triploid and Aneuploid Hybrids from Diploid-diploid Intergeneric Crosses between Citrus Cultivar 'Kiyomi' Tangor and Meiwa Kumquat (Fortunella crassifolia Swingle) for Seedless Breeding of Kumquats

In order to produce new seedless kumquat cultivars, we carried out an intergeneric cross between 'Kiyomi' tangor [Citrus unshiu Marcow. x C. sinensis (L.) Osbeck] and Meiwa kumquat (Fortunella crassifolia Swingle), obtaining 2 normal seeds and 7 undeveloped seeds. These seeds were cultivated on Murashige and Tucker medium, and the 2 normal seeds germinated and developed. The results of genome size analysis by flow cytometry revealed that both seedlings were triploids and that the difference in genome size corresponded to more than one chromosome in the 2 seedlings. Chromosome observation confirmed diploid (2n = 2x = 18) in both parents, aneuploid with 28 chromosomes (2n=28) for one of the seedlings, and triploid (2n = 3x = 27) for the other seedling. Random amplified polymorphic DNA (RAPD) and cleaved amplified polymorphic sequence (CAPS) analyses proved that the seedlings were intergeneric hybrids between 'Kiyomi' tangor and Meiwa kumquat, with the maternal organelle genome. These hybrids have the potential to be released as a cultivar after further tree and fruit evaluations, and for use as cross-parents in seedless kumquat breeding.