Classification of 'Tosa-Buntan' pummelo (Citrus grandis [L.] Osb.), 'Washington' navel orange (C-sinensis [L.] Osb.) and trifoliate orange (Poncirus trifoliata [L.] Raf.) chromosomes using young leaves

Chromosome samples of young leaves of 'Tosa-Buntan' pummelo (Citrus grandis [L.] Osb.), 'Washington' navel orange (C. sinensis [L.] Osb.) and trifoliate orange (Poncirus trifoliata [L.] Raf.) were prepared by the enzymatic maceration method. The preparations were sequentially stained with Giemsa, quinacrine mustard (QM), chromomycin A(3) (CMA), and 4'-6-diamidino-2-phenylindole (DAPI). The chromosome lengths and banding patterns among 4 staining methods were compared. The discrimination of centromeres was easier by QM staining than by Giemsa staining. By CMA staining, 5 characteristic banding patterns were observed. Therefore, 'Washington' chromosomes were divided into 4 groups, trifoliate orange chromosomes into 3 groups, and 'Tosa-Buntan' chromosomes into 5 groups. CMA staining enabled the confirmation of chromosome number as 18 in cells in which chromosome lengths were relatively long. Chromosome number in 'Washington' and 'Tosa-Buntan' were difficult to count by the Giemsa stain. We conclude that chromosome samples prepared by using young leaves and QM and CMA stainings are effective means to reveal chromosomes in citrus. Hence, a good possibility of karyotyping citrus in the future exists.