Effects of Gamma Irradiation on the Phenotype and Microbial Load of Lettuce (Lactuca sativa Linn.)

A mutation breeding study was conducted to determine the effect of four doses of gamma radiation (5 Gray, 10 Gray, 50 Gray, and 100 Gray) on the phenotype (color, weight, height, root length, and leaves surface area) and microbial load of lettuce (Lactuca sativa Linn.) grown from irradiated seeds under a controlled environment. Based on large effect size, 80% power, and 5% level of significance, 16 seeds per group/treatment were used in Completely Randomized Design involving five treatments (four doses and a control) and four replications. Normality and homogeneity of variance assumptions were checked and met. The alpha level was adjusted using Bonferroni correction for the five related ANOVA tests performed, excluding assessment for color which was based on color guide. No apparent color difference among treatment and control group was found. Statistically significant treatment effect was found for mean weight, mean height, mean root length, mean leaves surface area, and mean microbial load. Post hoc Tukey’s HSD test indicated that 100 Gray is the most effective dose in increasing mean weight, mean height, and mean leaves surface area and in decreasing microbial load. Ten Gray is the most effective dose in increasing mean root length. Keywords: Mutation breeding, gamma radiation, Lactuca Sativa Linn., phenotype, microbial load