Abstract
Six lines of Meiwa kumquat (Fortunella crassifolia Swingle) showing tetraploidy (No.5, No.6, No.8, No.12, No.18 and No.19), which had been induced by treating the nucellar embryos with colchicines, were investigated for ploidy level, origin and horticultural characteristics. Furthermore, these tetraploid plants were crossed with diploid kumquats for triploid production. All tetraploid plants were confirmed to be derived from the nucellar embryo of Meiwa kumquat by investigation of chromosome composition with chromomycin A3 staining. Flow cytometric analysis and chromosome observation of young leaves demonstrated that No.8 was a ploidy chimera that was both diploid and tetraploid. Five lines showing tetraploidy had the typical morphological characteristics of tetraploid Citrus plants, such as large leaves, flowers and pollen grains with low pollen fertility. However, these tetraploid plants have desirable traits for kumquat such as thicker pericarp, high sugar content and smaller number of developed seeds. No.8 had horticultural characteristics that were similar to those of tetraploid plants excluding the dermal system. When their polyploids were crossed with some diploid cultivars, triploid progenies were obtained from almost all cross combinations.
