Combining ability and heterotic patterns using Line × Tester analysis for yield under heat stress in tomato (Solanum lycopersicum L).

This study involved the crossing lines using a line × tester mating design, resulting in the production of 12 F₁ hybrids. The study was conducted at the Kaha Vegetable Research Farm, Horticulture Research Institute, Kaliobia Governorate. Both parental genotypes and their twelve crosses were assessed in an open field during the two consecutive summer seasons of 2022 and 2023. The study found significant differences in mean performance across all traits examined, attributable to the different genotypes. Highly significant differences existed among genotypes for all studied traits. lines × testers interaction was highly significant for all studied traits except number of days to 50% anthesis flowers (ND) and number of locule (NL). the estimated average degree of dominance (ADD) was higher than unity for five traits i.e., ND, fruit shape index (FSI), NL, total yield (TY) and total soluble solids (TSS), indicating that over dominance influenced the manifestation of these traits. Results from the general combining ability (GCA) effects analysis suggested that the line EL-S (P1) was a notable general combiner for fruit set % (FS), NF (number of fruit), NL and TY. The tester Saladette (P7) was a notable general combiner for FS, FW, FSI, NF and TY. The significant SCA effects for FS, NF and TY traits were obtained from the crosses P2 × P6, P2 × P7 and P4× P5. All crosses exhibited significant positive heterosis over better parent for TY except P2 × P5, P3×P5 and P3 × P6.