EFFECT OF POTASSIUM NITRATE ON THE PRODUCTION OF RICININE BY Ricinus communis AND ITS INSECTICIDAL ACTIVITY AGAINST Spodoptera frugiperda

Abstract

The effect of four nitrogen levels (KNO₃: 5, 10, 15 and 20 meq L^-1) on the production of ricinine was studied using a semi-hydroponic system. The insecticidal activity of methanolic extracts of Ricinus communis L. leaves against Spodoptera frugiperda Smith larvae was also tested. A dosage – response relationship showed strong positive correlation (R² = 0.92, P ≤ 0.05) between the nitrogen concentration in the hydroponic solution and ricinine percentage in leaves. A strong correlation (R² = 0.94, P ≤ 0.05) was also shown for nitrogen content in tissues and ricinine percentage. The use of nitrogen in the form of KNO₃ increased the production of ricinine, and it also affected mortality of S. frugiperda larvae. LC₅₀ for ricine methanolic extracts of R. communis leaves on S. frugiperda were 13,469.12, 15,754.34, 16,046.11 and 18,155.75 mg mL^-1 for nitrogen concentrations of 20, 15, 10 and 5 meq L^-1 respectively. Increased nitrogen concentration in the hydroponic solution associated with increments in leaf area and ricinine concentration. This indicates that nitrogen concentration can be manipulated to improve production of this alkaloid, and the extracts used for crop protection.