Classification of the Citrus Chromosomes with Same Types of Chromomycin A Banding Patterns

Abstract

Chromosomes were isolated enzymatically from young leaves of 'Tanikawa-Buntan' pummelo (an uncertain hybrid with Citrus grandis), 'Yoshida-Ponkan' mandarin (C. reticulata Blanco), 'Mukaku-Kishu' (C. kinokuni Hort. ex Tanaka), and sour orange (C. aurantium Linn.). The chromosomes were stained with Giemsa, chromomycin A₃ (CMA), and quinacrine mustard (QM). In CMA staining, five characteristic banding patterns (types A, B, C, D and E) were observed. The chromosome compositions with different CMA banding patterns were 3A+2C+4D+9E for 'Tanikawa-Buntan', 1B+1C+9D+7E for 'Yoshida-Ponkan', 1C+8D+9E for 'Mukaku-Kishu', and 1B+2C+8D+7E for sour orange. The chromosome composition in 'Mukaku-Kishu' was identical with koji (C. leiocarpa Hort. ex Tanaka). The sour orange had a type C chromosome with an elongated second constriction. Some chromosomes classified as the same CMA type exhibited different relative sizes in the CMA (+) regions. Type D chromosomes, which were not classifiable on the basis of chromosome lengths were categorized into two groups in 'Mukaku-Kishu' and three groups in the sour orange based on the relative sizes of their CMA (+) regions. Therefore, the relative sizes of CMA (+) regions are useful as indices for chromosome classification so that the relationships within the genus Citrus could be established.