CMA banding pattern of chromosomes is useful for the identification of chromosome doubling in haploid citrus

Abstract

A variant plant showing long internodes arose from a haploid plant obtained from clementine (Citrus clementina). Flow cytometric analysis and chromosome count revealed that it was a mixoploid with both haploid (2n = x = 9) and diploid (2n = 2x = 18) cells. The average length of the guard cells of the variant was almost the same as that of the haploid plant. This suggested that the epidermis of the variant consisted of haploid cells and that other leaf tissues consisted of diploid cells. Since in citrus the first germ layer forms the epidermis and the second and third layers form all the leaf tissues except for the epidermis, the variant was considered to be a ploidy periclinal chimera. When chromosomes of the young leaves were stained with chromomycin A 3 (CMA), they could be classified into four types based on the number and the position of the CMA-positive bands. The chromosome configuration of the variant differed from that of the original diploid clementine. The number of chromosomes of each type in the diploid cells of the variant was twice the number of those in the haploid plant. These results demonstrated that the diploid cells of the variant were doubled haploid cells, and that CMA analysis of chromosomes is useful for the identification of doubled haploids in citrus.