Gamma radiation induced genetic variability and physiological modulation in mutant litchi ( <i>Litchi chinensis</i> Sonn.) population

Mutation breeding has emerged as a powerful tool for expanding genetic variability and accelerating crop improvement, particularly in perennial fruit crops where conventional breeding is constrained by long juvenility and narrow genetic bases. The present study was conducted at the ICAR–National Research Centre on Litchi, Muzaffarpur, Bihar, India, from 2022 to 2025 to determine the median lethal dose (LD50) of γ-irradiation in litchi cv. Shahi and to assess induced morphological and physiological responses. Fresh seeds were irradiated in two phases using a Co60 γ-source: in 2022, with doses ranging from 5 to 50 Gy, which resulted in higher survival percentages and limited phenotypic variation; and in 2023, with higher doses ranging from 55 to 100 Gy to increase the mutation frequency. Survival percentage was recorded two months after sowing, and LD50 was calculated at 46 Gy. Morphological and physiological evaluations were subsequently conducted on mutant populations generated from irradiation doses above the estimated LD50 (46 Gy) to maximize mutation recovery and phenotypic variation. Analyses revealed that increasing irradiation doses reduced plant survival, height, canopy volume, and chlorophyll content, while inducing significant morpho-physiological alterations. Several novel phenotypes were identified, including a climbing-type growth habit, dwarfism, compact canopies, and altered leaf morphology. This study demonstrates the potential of gamma irradiation as an effective tool for creating selectable genetic variability and broadening the genetic base of litchi.