Chitosan Mediated growth,yield and bioactivities of sweet basil [Ocimum basilicum (L.)]

Abstract

The present study entitled “Chitosan mediated growth, yield and bioactivities of sweet basil (Ocimum basilicum L.)” was conducted at the Department of Plantation, Spices, Medicinal and Aromatic Crops, College of Agriculture, Vellayani, Thiruvananthapuram, Kerala during 2022- 2023 with the objective to evaluate the plant growth and biological activities of Ocimum basilicum L. in response to foliar application of chitosan at varying concentrations and frequencies. The seeds of O. basilicum used for the study were sourced from from Indian Institute of Horticultural Research, Bengaluru. The seeds were sown in portrays filled with potting mixture comprising of coir pith and vermicompost in the ratio 3:1. The 30-day-old seedlings were transplanted to grow bags and maintained organically up to 120 days after sowing (DAS). Chitosan was applied at varying concentrations (0.5 g L-1, 1 g L-1 and 2 g L-1) and frequencies viz., 15 days after transplanting (45 DAS) and 30 days after transplanting (65 DAS) to growbags. The experiment was laid out in completely randomized block design with fifteen treatments and three replications. The treatment consisted of base solution (chitosan 0 g L-1) sprayed at 15 DAT (T1), at 30 DAT (T2), at 15 & 30 DAT (T3), chitosan 0.5 g L-1 sprayed at 15 DAT (T4), at 30 DAT (T5), at 15 & 30 DAT (T6), chitosan 1 g L-1 sprayed at 15 DAT (T7), at 30 DAT (T8), at 15 & 30 DAT (T9), chitosan 2 g L-1 sprayed at 15 DAT (T10), at 30 DAT (T11), at 15 & 30 DAT (T12), water sprayed at 15 DAT (T13), at 30 DAT (T14), at 15 & 30 DAT (T15). The plant growth parameters viz., shoot length, number of branches, leaf area, collar girth and number of flowering branches were recorded at 30, 60, 90 and 120 days after sowing (DAS). The growth parameters exhibited a significant variation among the treatments. At harvest (90 DAS), the plants treated with chitosan 2 g L-1 at 15 & 30 DAT (T11) recorded the highest shoot length (59.37 cm) and number of branches (42), The highest 114 leaf area (8892.96 cm2) was observed in chitosan 1 g L-1 at 30 DAT (T8) and was on par with T11. The highest number of flowering branches was observed in treatment chitosan 2 g L-1 at 30 DAT (T11). The treatment chitosan 2 g L-1 at 15 & 30 DAT (T12) recorded early flowering (57.67 days). The data on yield parameters on leaf biomass, stem biomass and herbage yield were recorded at 90 DAS. The seed yield parameters viz., seed yield per plant and thousand seed weight were recorded at 120 DAS. The treatment chitosan 1 g L-1 at 30 DAT (T8) exhibited higher fresh leaf biomass (254.40 g per plant), dry leaf biomass (12.54 g per plant-1), fresh stem biomass (216.73 g plant-1), dry stem biomass (19.0 g plant-1), fresh herbage (485.24 g plant-1) and dry herbage (32.06 g plant-1) yield. The oil yield (210.36 g plant-1), seed yield (66.08 g plant-1) and test weight (10.57 g) were also observed to be maximum in treatment chitosan 1 g L-1 at 30 DAT (T8). The effect of chitosan on biochemical parameter, plant pigments were recorded at 30, 60, 90 and 120 DAS. The treatment T11 exhibited the highest chlorophyll and carotenoid content. The biochemical parameter, secondary metabolites viz., total alkaloids, flavonoids, total phenol content and tannins were recorded at 90 DAS and was found to be significantly influenced by the application of chitosan. The treatment T8 exhibited highest phenol (33.75 ug GAE mg-1) and alkaloid content (91.61 ug AE mg-1). The highest flavonoid and tannin content were recorded in the treatment T11. In HPTLC comparative chemical profiling analysis, the leaf extracts of O. basilicum showed 38 phytochemical constituents corresponding to specific Rf values. T8 had more number, 19 phytochemical constituents out of 38 total constituents recorded during the analysis. This was followed by T10 and T11 , which were observed to show 16 constituents among the 38 constituents recorded in the analysis. The treatment T8 (chitosan 1 g L-1 sprayed at 30 DAT) selected as the best treatment in terms of herbage and oil yield was compared with the corresponding control treatment, T14 (water sprayed at 30 DAT) to study the effect of chitosan on bioactivities. The study revealed that the defatted ethanolic leaf extract of T8 showed better performance in terms of antifungal (against Colletotrichum capsici MTCC 9691), antioxidant and enzyme 115 (peroxidase and catalase) activities compared to T14. Both the treatment (T8) as well as the control treatment (T14) did not show any antibacterial property when tried against Escherichia coli MTCC 40. The T14 leaf extract gave better cytotoxicity against HCT 116 colon cancer cell lines compared to that of T8. Among the treatments T8 (chitosan 1 gL-1 sprayed at 30 DAT) exhibited the best results in terms of yield, secondary metabolites and bioactivities. This was followed by T11 (chitosan 2 gL-1 sprayed at 30 DAT) with respect to these parameters. From the study it can be concluded that one time spray of chitosan 1 g L-1 at 30 DAT could be selected as the best treatment for enhancing yield, secondary metabolites and bioactivities of O. basilicum.