Somatic genetic analysis of the apical layers of chimeral sports in chrysanthemum by experimental production of adventitious shoots.

A B S T R A C T Many commercial chrysanthemum cultivars display unusual somatic variability. The 'Indianapolis' family of chrysanthemtum sports was analyzed for the genetic potential for color of each of the three layers in the apical meristem of their shoots. Populations of each cultivar were grown and sectors and off-color plants recorded. The location of the pigment within cells and between tissues was determined by microscopic examination of free-hand sections of fresh petals. Adventitiouis buds were forced from the stems of each cultivar by excising all normal lateral buds. These observations showed 12 of the 16 'Indianapolis' cultivars to be perielinal chimeras. Adventitious shoots often originated from two or more cells, derived from at least two different apical layers, and thuis were themselves periclinal chimeras. While somatic mutation is the ultimate source of the variability in 'Indianapolis' chrysanthemums, the most frequent type of sporting resulted from the loss in mitosis of a chromosome carrying a supressor for the formation of yellow chromoplasts, giving a yellow sector or shoot. Sectors resulting from rearrangement of layers in the