The aim of the study has been to assess the efficiency of choline-stabilized orthosilic acid (ch-OSA; bioavailabile form of silicon) application under increasing intensity of manganese stress on the chemical composition of plants and yielding of tomato (Lycopersicon esculentum Mill. cv. Alboney F1 and cv. Emotion F1). Plants were grown in rockwool with the application of a nutrient solution of the following chemical composition (in mg dm-3): N-NH4 2.2, N-NO3 230, P 50, K 430, Ca 145, Mg 65, Cl 35, S-SO4 120, Fe 2.48, Zn 0.50, Cu 0.07; pH 5.50, EC 3.00 mS cm-1. The following manganese levels in the nutrient solution were tested (in mg dm-3): 9.6 and 19.2. The effect of ch-OSA application (at a concentration of Si equal 0.3 mg dm-3 of the nutrient solution) was investigated at both Mn-levels. The ch-OSA application alleviated Mn toxicity by increasing the biomass production in the Mn-low variant (+ 8.2% for Alboney F1 and 16.8% for Emotion F1, the differences being significant for Emotion F1), whereas the ch-OSA application in the Mn-high variant did not influence the plant yielding. All the factors affected the plant nutrient status and the chemical composition of tomato fruits. The chemical composition of leaves depended on (means of all the studied combinations): Mn (K, Na) and ch-OSA nutrition (N, Mg, Na), cultivar (for P, K, Ca, Na), but in the case of fruits significant differences were found between Mn (N, P, Ca, Mg) and ch-OSA nutrition (N, Mg, Na) and cultivar (N, P). In both Mn-levels, visual symptoms of manganese toxicity appeared on plants – in the Mn-high variant, they were observed after 4 weeks, while in the case of the Mn-low variant - after 10 weeks of exposure to strong Mn-stress. Treatment with ch-OSA at both of the studied Mn levels did not prevent the development of visual toxicity symptoms on the plants.

20(4)2015