Growth, stomatal behavior, and photosynthetic pigment responses of sweet potato (Ipomoea batatas L) to different doses of gamma irradiation in M1V1 generation

Abstract

Induced mutation through physical mutagens, such as gamma irradiation is an effective and complementary breeding tool to enhance crop improvement by increasing genetic variation and creating heritable mutant alleles. This is highly important in crops such as sweetpotato, where genetic and reproductive constraints limit conventional improvements. This study was therefore designed to investigate the effects of gamma irradiation on the growth, stomatal behavior, and photosynthetic pigments of sweet potato (Ipomoea batatas L.) in the M1V1 generation. The experiment was conducted in a screenhouse in a randomized complete block design (RCBD) with twenty replications. Three sweet potato genotypes, Awassa-83, Alamura, and Kabode, were subjected to gamma irradiation doses of 0, 15, 25, and 35 Gray (Gy) to assess their median lethal dose (LD50), which was estimated via a probit model based on the seedling mortality rate, growth, stomatal behavior, and photosynthetic pigment responses. Significant differences (P < 0.05) were observed across varieties, doses, and their interactions for vine number, leaf number, internode length, vine length, and petiole length. The vine number was consistently reduced across the three varieties as the gamma dose increased to the maximum. The decline was 4.85 vines at 15 Gy in Alamura to Kabode’s 1.63 vines at 35 Gy. Similarly, the internode and vine length decreased with increasing dose across the varieties where Alamura scored the highest in both trait at 15 Gy but up to 30% decline in internode and 65% decline in vine length at the maximum dose of Kabode and Awassa-83, respectively. Stomatal traits response, including stomatal length and number, varied among the varieties with differing gamma dose following a non-linear pattern. Pigment analysis revealed that chlorophyll a, b and total chlorophyll was peaked in Awassa-83 and Alamura at 15 Gy before collapsing below 2 µg/ml at 35 Gy across all varieties. Carotenoids were moderately enhanced at 25 Gy in Awassa-83 (5.32 µg/ml) but declined sharply at 35 Gy. These findings highlight the potential of gamma irradiation in creating variation among the varieties for important traits. Further, the varieties responded differently to the gamma irradiation doses, showing genotypic differences. This helps to identify potential mutants in the subsequent generation for the traits studied and their physiological ramifications.