Morphological Variation in Plants Derived From in Vitro Culture of ‘Laura Bush' Petunia

‘Laura Bush' petunia, Petunia x violacea 'Laura Bush,' is a reseeding annual petunia that is available in a limited range of flower colors. Because somaclonal variation in a number of morphological features has been reported previously in petunia and other members of the Solanaceae, a project was undertaken to determine whether tissue culture could be used to isolate flower color variants of ‘Laura Bush' petunia with ornamental potential. Explants were excised from leaves of a single greenhouse-grown plant and cultured on Murashige and Skoog medium containing 4.4 µM BA using standard in vitro culture procedures. Microcuttings were harvested from shoot proliferating cultures after eight weeks, rooted under non-sterile conditions in plastic containers containing moistened Redi-earth, acclimated and then grown under standard horticultural practice in the greenhouse. A total of 880 plants were evaluated as they came into bloom. The rate of somaclonal variation estimated by visual scoring was 15%. Variants were grouped into several broad categories including leaf variegation, abnormally large leaves and flowers, severe stunting, fasciated stems, bilateral asymmetry of leaves, midvein abnormality, missing corolla segments, and abnormally small flowers. Large-leafed/large-flowered plants were the most prominent off-type (13%) with variegation occurring next most frequently (3%) and the remaining types occurring in less than 1% of the plants observed. Three types of variegated-leaf periclinal chimera were stabilized and are being cloned. No variation in flower color was observed.