Dose-dependent effects of gamma irradiation on in vitro regeneration, biochemical responses, and oxidative stress in two Begonia rex cultivars

This study aimed to optimize gamma irradiation for in vitro mutagenesis in two Begonia rex cultivars by determining lethal doses (LD 25 , 50, 75 ) and evaluating morpho-physiological responses and oxidative stress using the IBRv2 index. The ‌ in vitro -derived callus from leaf explants of two Begonia rex cultivars (“Jurassic” and “Silver King”) were exposed to seven gamma radiation doses (0.0, 10, 20, 30, 40, 50, and 100 Gy) in a 2 × 7 factorial completely randomized design with three replicates. Data were analyzed by two-way ANOVA followed by Duncan’s multiple range test ( P < 0.05). Based on regenerated plantlet survival, the estimated LD 25 , LD 50 , and LD 75 values for “Jurassic” were 43.05, 86.10, and 129.15 Gy, respectively, whereas the corresponding values for “Silver King” were 15.00, 60.00, and 105.00 Gy. Moreover, an increment in gamma radiation dose detrimentally affected plant height, root number, root length, leaf area, leaf number, growth index, and proliferation percentage. The quantities of total phenolic content (TPC) varied from 0.02 mg GAE/ g DW (for “Silver King” at 10 Gy) to 0.54 mg GAE/ g DW (for “Jurassic” at 40 Gy or 100 Gy). The highest ratios of total anthocyanin contents (TAC) were observed for “Jurassic” and “Silver King” cultivars at 40 Gy (1.35 and 1.65 times higher than controls). Both control and treated regenerated shoots of “Jurassic” showed maximum DPPH-assisted radical scavenging activity at 10, 40, and 100 Gy (92.9%, 92.6%, 91.2%, and 92.2%, respectively). For “Silver King”, 20 Gy and 100 Gy doses generated maximum scavenging activity (88.2% and 87.0%, respectively). Lastly, the maximum Integrated Biomarker Response version 2 (IBRv2) values of 24.88 and 30.43 were achieved for regenerated shoots of “Jurassic” and “Silver King” cultivars at 100 Gy, respectively, suggesting increased toxicity and greater oxidative stress due to gamma radiation. Overall, based on the estimated LD 50 and GR 50 values, a gamma irradiation dose of approximately 60–80 Gy is recommended for in vitro mutagenesis aimed at generating genetic variation in B. rex .