Determination of the effects of some lycopene-related genes on the ripening process in tomatoes

This study investigates the effects of certain genes known to influence lycopene content in tomatoes on the ripening process. Specifically, the genes High Pigment-1 (Hp-1), High Pigment-2 (Hp-2), Old Gold (Og), and Old Gold-crimson (Ogc), which are known to increase lycopene levels, were studied alongside one commercial determinate tomato variety. The study was conducted in two phases. In the first phase, tomatoes from five different genotypes were harvested at six different ripening stages, and various biochemical properties were compared. In the second phase, tomatoes from these five genotypes were harvested at the breaker stage and their ripening process at 20°C was analyzed. In both phases, the samples were evaluated for fruit firmness, soluble solids content (SSC), titratable acidity (TA), fruit color, total chlorophyll content, lycopene content, total phenolic content, and antioxidant activity. Additionally, weight loss changes were examined off-vine ripening of tomatoes. The genotypic effect on tomatoes has been shown to vary depending on the stage of ripeness. Genotypes with the hp-1 gene harvested at the red ripe stage exhibited higher fruit firmness. In terms of soluble solids content (SSC), tomatoes possessing the og and ogc genes were found to have higher values compared to those with the hp genes. Similarly, tomatoes with the og and ogc genes exhibited higher total titratable acidity (TTA). When examining color, tomatoes with the hp-1 and hp-2 genes displayed a deeper red hue. At the green ripe stage, tomatoes with the hp-2 gene had higher total chlorophyll content. Additionally, the reduction in chlorophyll content began later in tomatoes with the hp-1 and hp-2 genes compared to others. At the red ripe stage, the highest lycopene content was found in tomatoes with the hp-1 gene, followed by those with the hp-2 and og genes. Genotypes with the ogc gene harvested at the red ripe stage had higher total phenolic content than other genotypes, while those with the hp-1 gene showed higher antioxidant activity. Tomatoes harvested at the breaker stage and stored at 20°C exhibited higher weight loss in those with the hp-2 gene. After 15 days of storage, tomatoes with the og gene maintained a redder color. In terms of fruit firmness, those with the hp-2 gene remained firmer. The chlorophyll content also remained higher in tomatoes with this gene by the end of the storage period. Regarding SSC, tomatoes with the og and ogc genes had higher values than those with the hp-1 and hp-2 genotypes. By the end of the storage period, the lowest average lycopene content was found in the control and hp-1 genotypes, while the highest was observed in those with the og gene. The total phenolic content was higher in tomatoes with the ogc gene, whereas antioxidant activity was higher in both the ogc and hp-1 genotypes. The effects of genes influencing lycopene on the plant can differ from their effects during postharvest ripening. Therefore, in tomatoes with hp genes, known for their influence on lycopene, the onset of lycopene accumulation and color development occurs later and then rapidly increases compared to other genotypes. Considering different ripening stages, the hp-1 and hp-2 genes stand out in terms of color development and lycopene content. However, early harvesting of these genotypes for market supply might prevent the full realization of their potential at the red ripe stage. KEYWORDS: Tomato, Postharvest ripening, Quality, Lycopene, Ripening stages