Growth, yield and secondary metabolite elicitation in response to chitosan application in turmeric (Curcuma longa L.)

Curcuma longa L., is a rhizomatous, herbaceous plant belonging to Zingiberaceae family and has a wide range of pharmacological activities and cosmetic industrial value. Chitosan, extracted from fungal cell wall and crustacean shells is an emerging plant biostimulant that evokes growth promotion and metabolite elicitation. An experiment was conducted to study the effect of different concentrations and frequencies of foliar application of chitosan on plant growth, yield and secondary metabolite production in turmeric varieties, Sobha and Sona. The experiment was laid out in Randomized Block Design with three replications. The treatments included, F1: Chitosan 1 g/L monthly, F2: Chitosan 2 g/L monthly, F3: Chitosan 3 g/L bimonthly, F4: Chitosan 4 g/L bimonthly, F5: Chitosan 4 g/L trimonthly, F6: Chitosan 5 g/L trimonthly, Cp: Primed control and C: Unprimed control. The growth parameters were recorded at 6 months after transplanting (MAT) and yield at harvest. Curcumin content was analysed through HPTLC and expression profile of curcumin synthase gene was carried out by Quantitative Real-time PCR. Among the treatments, monthly application of Chitosan 2 g/L was observed to give better results in terms of plant height, leaf area, shoot weight and rhizome spread at 6 MAT. Monthly application of Chitosan 2 g/L, F2 and bimonthly application of Chitosan 4 g/L, F4 recorded significantly higher fresh rhizome yield per plant in variety Sobha (312.89 g and 322.85 g, respectively) and Sona (286.37 g and 284.06 g, respectively). Monthly application of Chitosan 2 g L-1 (F2) recorded a significantly higher curcumin content. The curcumin content enhanced by 89 % in Sobha and 54 % in Sona over the unprimed control. Chitosan treatment enhanced the expression of curcumin synthase gene by 1.48 fold in Sobha and 1.77 fold in Sona over control. Thus, monthly foliar application of chitosan 2 g/L gave better growth, yield, curcumin production and regulate curcumin synthase gene expression in turmeric in comparison to other frequencies and concentrations of chitosan.