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Compared to the studies on acute irradiation of seeds, fewer studies have reported on the chronic irradiation of seedlings, especially in fruit-bearing vegetables. We examined the effects of chronic gamma irradiation on tomato (<i>Solanum lycopersicum</i> ‘Micro-Tom’) seedlings exposed to gamma rays (50, 100, 150, and 200 Gy) for 4 weeks. As the total dose of gamma rays increased, leaf length, trichome density, and seed number were reduced in the irradiated seedlings (M₁). Additionally, a change in fruit shape was observed. Chronic gamma irradiation reduced the expression of two trichome-related genes and affected the expression levels of 11 reactive oxygen species (ROS)-related genes. We examined the transmittance of these effects using M₂ plants. The trichome density and fruit shape were similar between M₂ and control plants; however, a reduction in leaf length and seed number was detected in M₂ plants. Interestingly, changes in the expression of four ROS-related genes (<i>ZAT10</i>, <i>Mn-SOD</i>, <i>POD3</i>, and <i>RBOH1</i>) found in M₁ were detected in M₂ plants. Thus, the changes in phenotype and gene expression induced by chronic gamma irradiation were transmitted to the next generation. Additionally, we found novel mutants from M₂ plants, suggesting that chronic gamma irradiation may be considered in tomato mutation breeding.