M. I. Kamal, K. A. Zaied, A. M. AboAli, A. H. Abd El-Hadi Summer squash, earliness, ultraviolet irradiation, genetic variations, yield 30-42 8(2) 2024 April 2024 This study aimed to increase genetic variations in summer squash via mutation breeding as a strategy among traditional plant breeding techniques, to generate novel genotypes with increased yield and earliness to be helpful the grower–consumer interaction. Soaked seeds of four summer squash genotypes were irradiated with 0, 4, 8 and 12 minutes of ultraviolet rays (UV) rays. The seeds were sown in the field to rise the M₁ generation which was advanced to M₂ generation. The results of M₂ generation appeared highest decrease in the time of female flowering by Gen₃ irradiated with eight minutes. The highest fruit length was recorded by Gen₁ variety irradiated with 12 minutes of UV rays. Gen₃ exposed to four and eight minutes of UV rays produced significant increase in the number of fruits developed per plant in relation to unirradiated plants. The highest concentration of total chlorophyll in fruits was recorded by Eskandarani and Gen₁ treated with four minutes and Gen₁ treated with 12 minutes if compared with unirradiated plants. The doses of UV irradiation were significantly affected not only on the concentration of chlorophyll a in fruits but also on chlorophyll b in fruits. The interaction between genotypes by doses of UV irradiation were significantly affected on the concentration of chlorophyll a and total chlorophyll concentrations in fruits. Therefore, the results reflected that isolating of early maturing mutants with high earliness is possible at eight minutes of exposure time to UV irradiation.