THE EFFECT OF CESIUM 137 GAMMA RADIATION ON PLANT GROWTH AND FLOWER COLOR OF GREENHOUSE CHRYSANTHEMUM VARIETIES

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Abstract
The frequency and direction of color changes following gamma irradiation of the Indianapolis series of chrysanthemums provides evidence for the genetic nature of the chimeral tissue relationship in pink, white and bronze flowers. The process of widespread natural sporting is interpreted as being the result of infrequent cell substitutions between tunica layers through periclinal divisions and substitutions between the corpus and tunica in genetically heterogeneous varieties. Radiation induced color sports may arise either through cell substitution into damaged areas as in the color changes from pink to bronze, or through mass destruction of the tunica layers in the apical meristem, as in the color changes from pink to white, yellow and cream. The 2nd tunica layer appears especially sensitive to radiation effects. Since this tissue is gametogenic, such effects may contribute to an unfavorable environment for the selection of useful mutations in seed propagated species. In contrast, these same effects on clonally propagated species would be useful in revealing latent internal genetic diversity. The altered chimera might then be of sufficient value as an improved variety or as a parent in further breeding.