Pepino dulce (Solanum muricatum Ait.) of the family Solanaceae is native to the tropical and subtropical regions of the Andes. Pepino dulce fruit can be harvested at different stages of ripeness. As the majority of vegetables of the family Solanaceae, the fruit is abundant in potassium. Since there are no fertilizer recommendations for pepino dulce grown under cover, a study was launched to determine the fertilizer requirements of this vegetable. The aim of this study was to evaluate the effect of increasing magnesium rates and fruit ripeness stages on macronutrient content and ratios in the fruit of pepino dulce cv. Konsuelo. A two-factorial experiment in a completely randomized design was conducted in 2005-2007, in a tall, unheated, plastic tunnel at the Experimental Garden of the University of Warmia and Mazury in Olsztyn. Pepino dulce was propagated by cuttings taken from stock plants grown from seeds in 2004. The rooted cuttings were transferred to Kick- Brauchman pots filled with 9 dm3 mineral soil with pH 6.8. Experimental factors were as follows: I – Mg rates: 0.5, 1.0, 1.5 g Mg plant–1, II – fruit ripeness stages: ripe fruit showing a typical fully ripe color (yellowish-purple, yellow, cream), unripe green-colored fruit that has reached a typical form and size. The experiment was performed in four replications, and each replication comprised a pot with a single plant. Every pot was fertilized with 2 g N applied as CO(NH2)2, 3 g K applied as K2SO4 and increasing rates of Mg applied as MgSO4⋅7 H2O. Non-fertilized plants served as a control treatment. The plants were pruned for two stems. Fruit samples for chemical analyses were collected at full ripening (in mid-August). The concentrations of organic N, P, K, Ca and Mg in pepino fruit were determined, and the following weight ratios were calculated: Ca : P, Ca : Mg, K : Mg, K: (Ca + Mg), K : Ca. The results of chemical analyses were processed statistically by an analysis of variance (ANOVA), using Statistica 8.0 software. The highest total nitrogen and potassium levels were noted in the fruit of plants fertilized with the lowest magnesium rate (0.5 g Mg per plant), while the fruit of plants fertilized with the highest magnesium rate (1.5 g Mg per plant) accumulated the highest amounts of calcium and magnesium. The highest phosphorus content was reported in the fruit of non-fertilized plants. Fully ripe fruit contained significantly more nitrogen an magnesium, while unripe fruit had a higher content of phosphorus, potassium and calcium. An adequate Ca:Mg ratio, a narrow Ca:P ratio and wide K:Mg, K:(Ca + Mg) and K:Ca ratios were observed in all treatments.
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