Nitrate Reductase Drives Nutrition Control and Disease Resistance in Tomato (Solanum lycopersicum L.) Cultivars

Nitrate reductase plays an important role in preventing the occurrence of diseases and insect pests, which could rapidly reduce the accumulation of nitrate and induce the excess of soluble nitrogen compounds in plants. Tomato varieties “Myoko” (natural farming) and “Momotaro” (conventional chemical agriculture) were used in this study to show the positive correlation of the disease resistance and the enhanced nitrate reductase activity and the upregulated NR1, through the analysis of nitrate reductase genes, nitrate reductase activity. Disease resistance to early blight and mosaic virus was assessed, as was photosynthetic activity. Fruit yield and various biochemical parameters in fruit and leaves were determined. It was shown that Myoko F1 showed higher nitrate reductase activity compared to Momotaro, with significant differences seen in the expanding first leaf. This difference became more pronounced as the plants aged. Myoko and its parents exhibited higher NR1 expression than Momotaro. A modified Gaussian function model was used to simulate the expression trend, revealing significant differences between the tomato lines. The expression level of the NR1 and the daily average yield of tomato fruit during the growth period were simulated by the modified Gaussian curve equation (y = YM e−α(x−τ)^2 + YB (1 + βt)). Disease resistance to early blight was observed, with Myoko F1 showing higher resistance than Momotaro. The resistance was associated with higher nitrate reductase activity and NR1 expression. And the fruit yield showed that Myoko F1 had slightly higher yield potential than Momotaro due to its disease resistance. Myoko F1 inherited yield heterosis from its parents. Nitrate and amino acid concentrations in leaves were lower in Myoko F1, consistent with its higher disease resistance, nitrate reductase activity, and NR1 expression. At the same time, Myoko F1 exhibited higher concentrations of soluble sugars, organic acids, and vitamin C in tomato fruit compared to Momotaro, while nitrate concentration was lower. In addition, photosynthetic capacity (PC) was higher in Momotaro at the seedling stage but declined in the later fruit harvest period. Myoko and its parents maintained higher PC in the later stage, indicating better disease resistance and overall performance. In summary, Myoko F1’s prolonged optimal NR activity and NR1 expression, mediated by disease resistance, allow continued growth and yield despite biotic stressors. Further elucidating the connections between NR activity, senescence, and disease resistance will be valuable. Myoko F1 shows promise, but more work should explore its yield heterosis and suitability for fully natural, organic agriculture.