Investigation of the effects of organic and inorganic fertilization on quality, yield, content and gene expression levels in tomato (Solanum lycopersicum)

Tomato is a valuable vegetable globally and, in our country, used in various sectors and consumed in large quantities due to its rich nutrient content. To enhance tomato yield and quality, organic and chemical fertilizers are utilized. However, due to the adverse effects of chemical fertilizers on the environment and human health, there is a growing trend towards organic fertilizers. Vermicompost, obtained through the digestion of organic waste by worms, resulting in a nutrient-rich compost, is an example of organic fertilizers. Various criteria are used in determining tomato yield and quality. These can be classified as morphological, biochemical, and genetic factors. While the organic matter content of our country's soils is generally low, proper fertilization conditions lead to increased yield and quality. In this thesis study, two doses of vermicompost (54 g/plant (V1) and 108 g/plant (V2)) and two doses of inorganic fertilizer (NPK) (6.85 g/plant (F1) and 13.68 g/plant (F2)) were used to examine their effects on tomato yield and quality basing on soil analysis results and recommended dosages. Two different tomato varieties, 'Redguard' (RG) and 'Gülpembe' (GP), were utilized to investigate whether these fertilization treatments would differ among varieties and fertilization types. According to the results obtained from the study, in the RG variety, the high dose of vermicompost (108 g/plant) and the low dose of inorganic fertilizer (6.23 g NPK/plant), and in the GP variety, both doses of vermicompost (V1 and V2) increased yield to the same level compared to control plants. Both doses of inorganic fertilizer (F1 and F2) increased plant height, leaf number, stem fresh and dry weight and chlorophyll content, indicating their effectiveness in plant development. In the RG variety, the V2 treatment increased root fresh weight, root dry weight, and root length, while in the GP variety, inorganic fertilizer treatments (F1 and F2) increased root fresh and dry weights. The V1 treatment increased total phenolic content (TPC) and antioxidant content in leaf and fruit tissues for both varieties. Although no statistical difference was observed in fruit tissues, the highest values were obtained in leaf tissues, with 155.65 mg GA/100 g in the RG variety and 485 mg GA/100 g in the GP variety. Nitrite content in tomato fruits and leaves was not affected by fertilization practices. However, inorganic fertilizer treatments in both RG and GP varieties resulted in nitrate accumulation in leaves. In the GP variety, the high dose of vermicompost (V2) (108 g/plant) had a lycopene content of 16.52 mg/kg, yielding the highest lycopene content. PSY1, PSY2, and lyc-b are important enzymes in carotenoid and lycopene synthesis, and their gene expressions increased in fruit tissues under V1 treatment in both varieties. Gene expressions of genes involved in nitrate and nitrite assimilation (NR, Nii, and chlGS in leaves and GOGAT in roots) were higher in the RG variety under V2 treatment compared to controls, while in the GP variety, they were lower. This indicates that different varieties and fertilization practices may affect nitrate and nitrite uptake and utilization differently. The expression of the NRT2.1 gene, a nitrate transporter protein, increased in root tissues of the GP variety under all fertilization practices compared to controls. The higher nitrate content in GP variety leaves compared to control plants indicates effective transport of nitrate to tissues. In conclusion, vermicompost contributes to plant yield, while inorganic fertilizer contributes to plant growth. Including genes expressed at different levels in biotechnological studies aimed at developing varieties that utilize nitrogen more efficiently or perform better under organic fertilization conditions will provide valuable insights for both producers and breeders. This approach holds guiding significance, offering a pathway towards more informed and effective utilization of the genes in plant breeding. Furthermore, considering the adverse effects of intensive fertilizer use on the environment and human health, gaining a better understanding of the molecular and physiological basis of the effects of minimal fertilizer use or organic fertilizer applications will guide the development of environmentally friendly and healthy fertilization strategies without compromising yield and quality.