Somatic Genetic Analysis of the Apical Layers of Chimeral Sports in Chrysanthemum by Experimental Production of Adventitious Shoots

Abstract

A B S T RAe T 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 sterns 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. of selection and record-keeping by propagators, commercial plantings of the 'Indianapolis' chrysanthemum cultivars continue to contain a few plants of different color or habit, and some cultivars show divergent branches or sectors. The offtype plants and sectors have been too frequent to be accounted for by somatic mutation alone. The present study was undertaken in an attempt to understand or explain the somatic variability of the chrysanthemum.MATERIALS AND METHODs-Rooted cuttings from regular commercial propagator's stock of 16 IND cultivars were furnished by Yoder Brothers, Inc. .Barberton, Ohio over a period of 3 years. The family tree of the IND family of sports has been published recently (Yoder Bros., Inc., 1967) showing the sequence of origin of the different members. Three separate lots totaling about 100 plants of each cultivar were flowered under standard forcing schedules, one flower per stem, and the flowers observed for trueness to cultivar color and for sectors of different color. From one shipment of cuttings, 25 plants of each cultivar were planted individually in 4-in. pots and kept under continuous illumination. Two weeks after potting, the plants were cut back to approximately ten nodes, and all the visible lateral buds were excised. Latent lateral buds were excised when forced into growth and after approximately 6 weeks no more buds developed. After about 10 weeks growths of different character were observed and their development followed from inception with notes and photographs. As these growths developed into shoots 1061 1

Stability of Leaf Variegation in Saintpaulia ionantha During In vitro Propagation and During Chimeral Separation of a Pinwheel Flowering Form

“…Several authors have reported the production of chimera1 plants formed adventitiously on chimera1 tissues. In Chrysanthemum Stewart and Dermen (1970) reported the production of 27 chimera1 out of 80 adventitious shoots formed on dis budded stems ofchimera1 cu1tivars. This is an unusually high percentage compared to most other plants reported in the literature.…”

Competition and Accommodation Between Apical Layers and Their Derivatives in the Ontogeny of Chimeral Shoots of Pelargonium X Hortorum

“…G-DplcG leaves were as large as G-G-G, and the amount of green tissue from L-III was the same as the amount of white tissue in a G-G-DpI1 leaf. In the anthocyanin mutant in Euphorbia (Stewart and Arisumi, 1966), the bracts were the same size and shape whether none, one, two, or all three layers were mutant. In chrysanthemum (Stewart and Dermen, 1970b) the various chimeral combinations of mutant chromoplast and/ or anthocyanin layers were alike except for color.…”

“…Such differences were shown in stem, leaf, stipule, pedicel, calyx, and ovary. Clowes (1961), Bergann and Bergann (1962), Tilney-Bassett (1963), Dermen (1965), Neilson-Jones (1969), and others described periclinal chimeras in which the growth was obviously abnormal and from which few useful ontogenetic conclusions could be drawn.…”

“…Cell lineages are easier to follow in chloroplast chimeras than in cytochimeras and extensive observation of cell lineages in the mature plant structures is possible. Recent papers (Burk, Stewart, and Dermen, 1964;Stewart and Arisumi, 1966;Stewart and Dermen, 1970a;Stewart and Burk, 1970;Stewart, Meyer, and Dermen, 1972) have pointed out the potential uses of pigment chimeras in ontogenetic studies and described various features of the growth and development of the stem and its appendages in a number of species.…”

Plantlets from Petal Segments, Petal Epidermis, and Shoot Tips of the Periclinal Chimera, Chrysanthemum morifolium 'Indianapolis'

“…Plants consisting of only the genotype of layer I do not resemble the usual 'Indianapolis' chrysanthemum because "the character of some of the cultivars is inherent in their chimeral nature. When adventitious shoots were obtained which are not chimeral this unique characteristic may be lost or altered" (Stewart and Derman, 1970).…”