Metabolic Response of ‘Topaz’ Apple Fruit to Minimal Application of Nitrogen during Cell Enlargement Stage

Abstract

Nitrogen is an integral element of foliar sprays during apple fruit formation. However, in red cultivars, the application may have adverse effects on color in the second stage of fruit development. The effect of a low-dose foliar application of urea was monitored on ‘Topaz’ apple pomometric (fruit mass, firmness, total solids, starch content, skin color) and biochemical traits (primary metabolites, phenolic compounds, and assimilatory pigments). Three applications (17 July, 27 July, and 18 August) of two different urea doses (N1 = 1.4 kg N ha−1; N4 = 4 kg N ha−1) and control (N0, only sprayed with water) were used. Low doses of urea did not affect flesh firmness, total soluble, solid, and starch content, but individual fruit mass was significantly higher in N1 treatment compared to the other two treatments. Significantly lower a* parameters and a lower content of anthocyanins were measured on apples subject to N4 treatment. Many secondary metabolites (phenolic acids, flavan-3-ols, flavonols, and chalcones) were also negatively affected by low-dose urea application. Conversely, urea treatments significantly increased total assimilatory pigments in apple skin. Even minor levels of nitrogen, applied directly on the leaf at later stages of red apple fruit development, negatively altered color traits and the composition of metabolites.

Influence of Living Mulch and Nitrogen Dose on Yield and Fruit Quality Parameters of Malus domestica Borkh. cv. ‘Sampion’

“…Fruit quality parameters, such as size and color, as well as their flavor and taste, are important sensory attributes for consumers [24]. In apples, fruit color is mainly determined by anthocyanins [25], which increase when the tree is deprived of excessive amounts of nitrogen and has moderate growth [26]. Nitrogen dose should also improve fruit size and impact more significantly in secondary rather than on primary metabolism.…”

Metabolite Diversity in Pulp Segments, Peel, Leaves, and Bark of a Red-Fleshed ‘Baya Marisa’ Apple Cultivar

“…These compounds are very important for a plant's growth and development. Their synthesis is genetically predefined and cultivar-specific or boosted as a response to the plant's environment [5]. Sugars, organic acids and phenolics define inner fruit quality traits, and several groups of secondary metabolites (for example, anthocyanins) considerably affect apple fruit appearance.…”

Transcriptome and Metabolome Studies on Pre-Harvest Nitrogen Impact on Fruit Yield and Quality of Peach (Prunus persica L.)

“…Previous studies have found that increasing N supply from the blooming stage to three weeks before maturity resulted in improved leaf N status and photosynthetic activity, generating faster cell proliferation and larger ‘Gala’ apple fruit [ 10 ]. However, another study found that low doses of urea had no effect on flesh firmness, total soluble solids, or starch content during the cell enlargement stage in apple plants [ 11 ]. In mango, a higher proportion of N applied 2 or 4 weeks prior to harvest was able to increase the growth of leaves and stem, while low rates of N applied prior to harvest increased stem biomass only [ 12 ].…”