American Journal
of Botany 57(9): 1061-1071 (Oct 1970)
Somatic Genetic
Analysis of the Apical Layers of Chimeral Sports in Chrysanthemum by
Experimental Production of Adventitious Shoots
R. N. Stewart
and Haig Dermen
Abstract
Many commercial
chrysanthemum cultivars display unusual somatic variability. The `Indianapolis'
family of chrysanthemum 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. Adventitious
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
periclinal chimeras. Adventitious shoots often originated from two or more cells,
derived from at least two different apical layers, and thus 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 periclinal chimeras were
less frequent than the sectors from chromosome loss.