Growth, yield and curcumin production in turmeric (curcuma longa L.) mediated by chitosan application

Abstract

The research programme entitled “Growth, yield and curcumin production in turmeric (Curcuma longa L.) mediated by chitosan application” was carried out in the Department of Plantation, Spices, Medicinal and Aromatic Crops, College of Agriculture, Vellayani, during 2021 to 2023 with an objective to evaluate the effect of different modes and frequency of application of chitosan (CTS) on plant growth, yield and secondary metabolite production in Curcuma longa. The present study was carried out as four experiments (i) Biopriming of rhizome bits using chitosan (ii) Effect of different modes and frequency of application of chitosan (iii) Effect of chitosan application on beneficial soil microflora and (iv) Effect of chitosan application on expression profile of curcumin synthase gene. All the experiments were tried in two varieties viz., Sobha and Sona. In the first experiment, single bud rhizome bits were treated with different concentrations of chitosan for specified periods. The experiment was laid out in Completely Randomized Design (CRD) with three replications. Each replication consist of 25 rhizome bits. The treatments included, T1: CTS 1 g L-1 for 30 min, T2: CTS 1 g L-1 for 1 h, T3: CTS 2 g L-1 for 30 min, T4: CTS 2 g L-1 for 1 h, T5: CTS 4 g L- 1 for 30 min, T6: CTS 4 g L-1 for 1 h and T7: Control (without priming). The treated rhizome bits were shade dried and sown in protrays and maintained for 45 days. The observations on growth parameters were recorded at 45 days after planting. The rhizome bits exposed to CTS 1 g L-1 for 1 h was observed to give better results in terms of growth parameters and vigour index in both the varieties. Chitosan treatment enhanced the shoot length of the plantlets by 58 % in Sobha and 83 % in Sona, over the control. The collar girth enhanced by 39 % and 19 % over the control in Sobha and Sona, respectively. However, the chitosan treatment did not significantly influence the days to sprouting, sprouting per cent and survival per cent in both the varieties. The plantlets obtained on priming of rhizome bits with CTS 1 g L-1 for 1 h was used to study the effect of different modes (foliar and soil application) and frequency of application of chitosan in the second experiment. The experiment was laid out in Randomized Block Design (RBD) with three replications. The foliar application treatments included, F1: CTS 1 g L-1 monthly, F2: CTS 2 g L-1 monthly, F3: CTS 3 g L- 1 bimonthly, F4: CTS 4 g L-1 bimonthly, F5: CTS 4 g L-1 trimonthly, F6: CTS 5 g L-1 trimonthly, Cp: Primed control and C: Unprimed control. Chitosan application significantly influenced growth, quality and yield parameters of turmeric over the control. Among the foliar treatments, monthly application of CTS 2 g L-1 (F2) was observed to give better results in terms of plant growth parameters viz., plant height, leaf area, shoot weight, rhizome spread and rhizome weight at 6 MAT. The cell membrane integrity and total chlorophyll content was observed to be significantly higher with monthly application of CTS 2 g L-1 (F2) in both the varieties. The activity of defense enzymes (peroxidase and polyphenol oxidase) were significantly higher in F2, in Sobha and Sona. F2 and F4 recorded low incidence of leaf blotch disease. Chitosan application significantly influenced the yield and yield attributing characters compared to untreated control. Trimonthly foliar application of CTS 4 g L-1(F5) and trimonthly foliar application of CTS 5 g L-1 (F6) recorded significantly higher dry yield per plot (1.93 kg) in variety Sobha, which was on par with all other chitosan foliar treatments. In variety Sona, bimonthly application of CTS 4 g L-1 (F4) recorded significantly higher dry yield per plot (2.21 kg) and on par with all other chitosan foliar treatments except F1. Foliar application of chitosan enhanced the dry yield in the range of 43 % to 69 % in Sobha and 56 % to 91 % in Sona over the control. Nutrient uptake also recorded a significantly higher value in F2 in both the varieties. In foliar spray treatment, F2, F4 and F6 recorded significantly higher volatile oil content in Sobha, while in Sona F2 and F4 recorded higher values. Oil content enhanced by 116 % to 137 % in Sobha and 144 % to 164 % in Sona over the control. F2 and F4 recorded significantly higher oleoresin content in both the varieties. Oleoresin content increased in the range of 76 % to 82 % in Sobha and 64 % to 72 % in Sona compared to control. F2 (6.63 %) and F4 (6.42 %) recorded higher curcumin content and enhancement ranged from 83 % to 89 % in Sobha. While in Sona, F2 recorded higher curcumin content (7.35 %) which recorded an enhancement of 54 % over the control. From the study it could be concluded that the best priming treatment of rhizome bits is with CTS 1 g L-1 for 1 h in terms of seedling growth and vigour index in both the varieties. All the chitosan treatments gave better performance in terms of yield over the control irrespective of mode of application in both the varieties. F2 and F4 gave better performance with respect to both yield and quality. Among these, the BC ratio was observed to be higher in F4 in both the varieties. Hence, F4 (bimonthly foliar application of CTS 4 g L-1) is selected as the best and economically feasible chitosan treatment for improving growth, yield and secondary metabolite production in turmeric. Chitosan application also improved the population of beneficial soil microflora, nitrogen fixing bacteria and phosphorus solubilising bacteria. Chitosan also enhanced the expression level of curcumin synthase gene.