The 2012 ASHS Annual Conference

Forsythia × ‘Meadowlark’, released by North Dakota State University and South Dakota State University, in collaboration with the Arnold Arboretum and the North Central Regional Plant Introduction Station, Ames, IA, is an extremely hardy flowering shrub (flower buds have shown hardiness at -30 to -40 F) and widely planted for northern landscapes. It might be the first field flower in the spring in North Dakota and northern Minnesota. This shrub is very tolerant to drought and pests. It grows rapidly and can easily reach a height of 7 to 10 feet. However, the large stature is one of the concerns because it grows too big to fit in a limited space in residential areas. In this study, mutagenesis by gamma ray irradiation was employed to induce genetic variations. In vitro shoot tips of Forsythia × ‘Meadowlark’ was exposed to 0-100 Gy gamma rays and then recovered in MS (Murashige and Skoog, 1962) medium supplemented with 2.5 µM benzyladenine (BA). Shoots that survived from the gamma ray treatment were rooted in ½ MS medium containing 0.5 µM naphthalene acetic acid (NAA). An average of 80.3 % of shoots were rooted /recovered from the 25 Gy gamma ray treatment followed by 36.5, 5.4, and 2.1% from the 37, 50, and 70 Gy irradiation treatments, respectively. No shoots were survived when exposed to 100 Gy gamma rays. Rooted plants were transferred to potting mix and grown in the greenhouse for 3-5 months and then transplanted in the field. Morphological variations were first screened in the greenhouse and then in the field. Treated plants showed certain degree of reduced growth in the greenhouse. Various variations including characteristics of leaves (shape, size, hairs), stems (shape, internode length, branching), and plant stature were observed. These variations will be further screened in the field. This research demonstrates that in vitro mutation induction using gamma ray irradiation could be a useful protocol to develop new cultivars or genetic materials for further breeding of Forsythia or other related species.