Effect of Gamma Irradiation on Morphological Traits of Cassava (Manihot esculenta L. Crantz) Genotypes

Cassava (Manihot esculenta L. Crantz) is a perennial shrub characterized by outcrossing and a long breeding cycle, and significant inbreeding depression. Cultivated genotypes of cassava exhibit high heterozygosity; however, their reliance on vegetative propagation limits genetic diversity. To harness the inherent heterozygosity of cassava, the application of physical mutagens, specifically gamma irradiation, has been an effective method for generating novel genetic diversity, surpassing the slow and infrequent spontaneous mutation. The objective of the study was to create variation among candidate genotypes and determine the optimal doses for the effective mutagenic impact of gamma irradiation. Three cassava genotypes were exposed to gamma irradiation doses of: control (0), 15, 25, and 30 Gy. For seven months, we assessed the growth characteristics of cassava genotypes following gamma irradiation. Notably, the CAS-1 genotype showed a reduction in leaf lobes at 25 Gy. We successfully identified the LD50 and GR50 values for CAS-2 and CAS-3 genotypes at 23.62 Gy/23.05 Gy and 14.37 Gy/25.84 Gy, respectively; however, values for CAS-1 could not be determined due to suboptimal testing doses. Our analysis indicates optimal irradiation doses for CAS-2 and CAS-3 fall between 14 and 25 Gy. Additionally, a stimulating effect on sprout height was noted for CAS-2 at 15 Gy and CAS-1 at 30 Gy. Overall, while higher irradiation doses were detrimental to survivability in CAS-2 and CAS-3, CAS-1 demonstrated an increased survival rate. Our findings emphasize the importance of routine radiation sensitivity tests for all mutation breeding materials given their genetic variabilities.