Improvement of Landscape Plants Using In Vitro Mutation Method

Mutation breeding has proven as an established method for development of novel cultivars of many horticultural plants. However, the appearance of chimeras after vegetative propagation for several times seems a major concern of mutation breeding because mutations often occur in a small portion or an aggregate of cells mounded in the normal tissues and will never be identified. In vitro techniques might be the key to solve the problem. For example, multiple-micropropagation using existing buds will speed up the establishment of stable periclinal chimeras within a short time period; In vitro plant regeneration from single undifferentiated cell lines may circumvent problems associated with the formation of chimeras. In this study, induction of mutations by treating in vitro tissues of several ornamental plants with ethyl methanesulfonate (EMS) and gamma ray has been attempted. Concentration of EMS and treatment time and the dosage of gamma ray have been determined based on LD₅₀ (half of treated explants survived). Preliminary results showed that in vitro shoot tips survived after treated with EMS at 5 to 50 mM for 0.5 to 6 hr; however, growth of the plants treated with high EMS (> 25) for more than 2 hr was dramatically inhibited and some plants eventually died. Shoot tips of Physocarpus opulifolius ‘Center Glow’ exposed to gamma ray died in two months when the dose was greater than 100 Gy. The EMS-survived plants grown in the greenhouse showed phenotypic variations (leaf shape, color, and plant stature). To date, approximately 80, 300, and 200 plants obtained from EMS-treated Forsythia x ‘Meadowlark’, Physocarpus opulifolius ‘Center Glow’, and Cornus sericea ‘Cardinal’, respectively and more than 100 Physocarpus opulifolius ‘Center Glow’ plants survived from gamma ray treatment, are being screened for useful mutants under both field and greenhouse conditions.