Effects of gamma radiation (⁶⁰Co) on the in vitro mutation of the Son La ancient chrysanthemum variety (Chrysanthemum sp. “Cuc Son La”)

Abstract

The Son La ancient chrysanthemum, a woody-stemmed variety, is prized for pot cultivation and bonsai, reflecting the cultural significance of chrysanthemums as symbols of longevity. This study, conducted from February to November 2024 at Nong Lam University, Ho Chi Minh City, aimed to evaluate the impact of gamma radiation (⁶⁰Co) on the in vitro propagation and mutation induction of Son La ancient chrysanthemum plants, thereby identifying the optimal radiation dose for mutation breeding. The experiment was carried out using a completely randomized design with a two-factor setup: tissue type (shoot clusters, callus) and radiation dose (0, 20, 30 and 40 Gy). Results showed significant impacts on survival, growth, and mutation frequency. The LD50 (lethal dose, 50%) values at 50 days after irradiation (DAI) were 36.8 Gy for shoot clusters and 16.0 Gy for callus, indicating higher callus sensitivity. In shoot clusters, 20 Gy significantly stimulated growth (6.1 shoots, 6.2 cm height, 43.4 leaves), while 40 Gy severely inhibited it (2 shoots, 1.1 cm height, 8.9 leaves); callus survival sharply declined at 20 Gy (31.1%) and reached 0% at 30 and 40 Gy. A dose of 20 Gy induced diverse morphological mutations in shoot clusters (leaf color, shape, stem), while 40 Gy caused 100% yellowing and stunting; callus primarily showed chlorophyll loss (6.9%) and shoot regeneration failure (15.6%). Statistical analysis revealed a significant tissue type-dose interaction (P < 0.01). A dose of 20 Gy was optimal for mutation induction in shoot clusters, whereas callus being too sensitive. This study provides new LD50 data, tissue-specific radiation sensitivity, and mutation potential, recommending 20 Gy for future breeding studies focusing on shoot clusters, and suggesting further investigation into shoot cluster radiation tolerance.