Increasing the content of leaf and root alkaloids of high alkaloid content mutants of periwinkle through nitrogen fertilization

In industrial plants such as medicinal plants, the content of the economically important metabolite is more important than the yield of the plant part containing the metabolite, as it determines the cost of extraction of the metabolite. Two high alkaloid content mutants of periwinkle (Catharanthus roseus, a medicinal plant yielding anti-cancer and anti-hypertension alkaloids) were developed through induced mutagenesis. Since the availability of nitrogen (N) is expected to play an important role in the biosynthesis and accumulation of alkaloids in plants, the effect of N fertilization on the content of alkaloids of two high alkaloid content mutants of periwinkle was studied, in comparison with their parental variety, Nirmal, to determine the possibility of further increasing their alkaloid contents. The three genotypes were evaluated at three levels of N (0, 100 and 150 kg ha⁻¹) fertilization in a split plot experiment, which was repeated over 2 years. N fertilization significantly increased the content of alkaloids both in leaves and roots of all genotypes. Over genotypes, application of 150 kg ha⁻¹ of N resulted in an increase of 42 and 32% in the content of leaf and root alkaloids, respectively. However, the increase was highest in genotypes with the lowest content of leaf or root alkaloids. The high alkaloid mutants grown at 150 kg ha⁻¹of N fertilization exhibited an increase of 87 and 56% in the content of leaf and root alkaloids, respectively, when compared with their parental variety grown without nitrogen fertilization. N fertilization increased leaf and root yields by 170 and 90%, respectively. The increase in contents of leaf and root alkaloids, due to N application, paralleled the increase in leaf and root yields.