Effect of biostimulants and phytohormones on growth, herbage yield, and physio-biochemical characteristics of sweet basil plants under drought stress | |
| Author | Biswas, Arindam |
| Call Number | AIT Diss. no.AS-25-02 |
| Subject(s) | Plants--Effect of drought on Plant growth promoting substances Plant biotechnology |
| Note | A Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Agricultural Systems and Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | Drought is one of the severe abiotic stresses, causing higher annual crop loss than all plant pathogens combined. Sweet basil (Ocimum basilicum L.), a widely valued medicinal and aromatic plant, is particularly vulnerable to drought stress, which negatively impacts its growth, marketable yield, and essential oil content. In commercial basil production, drought stress significantly limits biomass accumulation and disrupts the biosynthesis of secondary metabolites. Biostimulants and phytohormones have emerged as promising tools to enhance the resilience of sweet basil plants to drought stress. Among them, silicon (Si), salicylic acid (SA), gibberellic acid (GA3), and methyl jasmonate (MeJA) have individually demonstrated the ability to mitigate drought-induced damage by improving plant growth, physiological responses, and yield. This investigation aimed at evaluating the combined effects of Si either with SA, GA3, or MeJA in improving drought resilience in sweet basil. Given their known individual benefits, it was hypothesized that combining these treatments may further enhance biomass production, physiological resilience, and secondary metabolite biosynthesis under drought stress. Therefore, a series of polyhouse experiments were conducted in order to explore these interactions that could provide valuable insights for optimizing the use of biostimulant and phytohormone in basil cultivation, ensuring higher productivity and quality even under water-limited conditions.The first experiment focused on assessing the effectiveness of selected biostimulants applied as seed priming materials on growth, herbage yield, and physio-biochemical composition of sweet basil exposed to drought stress. The seeds of sweet basil were primed with six agents (hydropriming, silicon (Si), salicylic acid (SA), gibberellic acid (GA), methyl jasmonate (MeJA), and chitosan (CHI)) and non-primed seeds were used as the control. Plants were subjected to three levels of soil water exposure (50, 75, and 100% field capacity (FC)). Seeds primed with GA and MeJA outperformed the non primed control in all investigated parameters by increasing germination parameters, growth, herbage yield, and biochemical properties. An increase of 10–24% and 35 66% in height and leaf area of plant, respectively, was observed from MeJA-treated plants than the non-primed control plants, while GA-priming treatment enhanced leaf number per plant, aboveground biomass, herbage yield, irrigation water productivity,leaf relative water content, free proline content, net photosynthetic rate, stomatal conductance, total phenolic content, and total flavonoid content by 11–47%, 15–23%, 16–47%, 21–50%, 6–30%, 90–180%, 19–55%, 26–50%, 25–35%, and 46–67%, respectively, regardless of soil water contents. Seed priming with GA and MeJA could be an effective strategy for enhancing the performance of sweet basil plants grown either in well-watered or water-stressed conditions.The second polyhouse study aimed at evaluating the efficacy of Si and SA, both independently and in concert, in mitigating the deleterious impacts of drought stress on sweet basil plants. A factorial experiment was implemented using a completely randomized design, incorporating soil application of three Si levels (0, 30, and 60 kg ha–1), foliar application of three SA levels (0, 100, and 200 mg L–1), and three soil moisture levels (50, 75, and 100% FC). Leaf area, shoot dry matter, leaf yield, irrigation water productivity, net photosynthetic rate, and stomatal conductance were declined by 54–78%, 55–66%, 77–84%, 55–68%, 42–70%, and 73–92%, respectively, at 50% FC in contrast to conditions at 100% FC, while electrolyte leakage, free proline concentration, total phenol concentration, and total flavonoid concentration were increased by 77–130%, 173–330%, 87–148%, and 101–169%, respectively, across Si and SA doses. The treatment of 60 kg Si ha–1 in conjunction with 100 mg SA L–1 emerged as the most efficacious treatment. This combination resulted in a 174% augmentation in leaf area, a 91% enhancement in shoot dry matter, a 98% increase in leaf yield, a 63% increase in irrigation water productivity, a 28% rise in leaf relative water content, and a 112% increase in total phenol concentration at 50% FC, when compared to plants grown under the same soil moisture level without Si and SA supplementation. Additionally, this treatment combination reduced electrolyte leakage by 26% compared to the plants not receiving Si and SA at 50% FC. The performance of plants under this combination at 75% FC was superior to that of the control plants even under optimal conditions at 100% FC for some parameters, underscoring the drought-mitigating potential of Si and SA in sweet basil. The combination of Si (60 kg ha–1) as a soil amendment and SA (100 mg L–1) applied as a foliar spray could be an effective strategy for improving the drought tolerance ability of sweet basil and enhancing its performance under both water-stressed and well-watered conditions.The objective of the third experiment was to discern the potential of soil application of Si and foliar application of GA3, both individually and in combination, in alleviating the adverse consequences of water scarcity on sweet basil. The study was conducted under a completely randomized design with three factors, such as soil application of three Si doses (0 [Si0], 30 [Si30], and 60 [Si60] kg ha–1), foliar application of three GA3 doses (0 [GA3-0], 50 [GA3-50], and 100 [GA3-100] mg L–1), and three soil water regimes (FC 50%: FC50, 75%: FC75, and 100%: FC100). Shoot length, dry weight of shoot, leaf number, herbage yield, water productivity, solute potential (Ψs), and net photosynthetic rate (Pn) were declined by 27–33%, 53–58%, 41–45%, 67–73%, 52 68%, –0.26 to –0.49 MPa, and 39–58%, respectively, at FC50 in comparison to FC100 across Si and GA3 doses. The combined soil supply of Si30 and foliar application of GA3-50 was the most effective treatment, leading to a 31% increase in leaf area, a 91% rise in herbage yield, an 86% enhancement in water productivity, a 149% increase in Pn, a 96% rise in total phenol concentration, and a 186% boost in total flavonoid concentration at FC50 as compared to those plants raised under similar soil moisture level without Si and GA3 supplementation. Moreover, the performance of some parameters of the plants treated with the same combination at FC75 was better than the control plants grown at optimal conditions of FC100, underlining the drought-alleviating potential of Si and GA3 in the cultivation of sweet basil. Exogenous application of Si30 as a soil supplement and GA3-50 as a foliar spray appears to be a promising technique for enhancing drought resilience of sweet basil plants and optimizing its growth potential in both well-irrigated and water-stressed conditions.The fourth study was aimed at evaluating the potential of soil-applied Si and foliar applied MeJA, used separately and together, to mitigate the negative impacts of drought on sweet basil. A polyhouse experiment was conducted in a completely randomized design including three factors, such as three Si doses (0, 30, and 60 kg ha–1), three MeJA doses (0, 0.25, and 0.50 mM), and three soil water content levels (50%, 75%, and 100% FC). A significant reductions in shoot height (23–40%), leaf area (56–67%), shoot dry matter (29–51%), fresh shoot biomass (53–58%), fresh herbage yield (51–64%), water productivity (29–39%), net photosynthetic rate (23–50%), and stomatal conductance (33–67%) were observed at 50% FC as compared to 100% FC across varying doses of Si and MeJA. The combined application of 60 kg Si ha–1 and 0.25 mM MeJA outperformed all other treatment combinations, resulting in an increase of 82% in leaf area, 121% in fresh herbage yield, 158% in shoot dry matter, 64% in water productivity, 208% in net photosynthetic rate, 61% in phenolic concentration, and 138% in flavonoid concentration at 50% FC as compared to the untreated plants under the same soil moisture conditions. This combination demonstrated superior plant performance at 75% FC for certain parameters as compared to the control plants grown at 100% FC, highlighting the drought-mitigating potential of Si and MeJA in sweet basil production. These findings indicate that applying Si (60 kg ha–1) to the soil and MeJA (0.25 mM) as a foliar spray may be a promising strategy to enhance drought resilience and optimize growth of sweet basil under both optimal and water-limited conditions. Drought stress significantly reduces growth, yield, water productivity, and physiological traits in sweet basil, leading to substantial biomass loss and disruption of secondary metabolite biosynthesis. This study highlights the potential of biostimulants and phytohormones, particularly silicon (Si), salicylic acid (SA), gibberellic acid (GA₃), and methyl jasmonate (MeJA) in enhancing drought tolerance through improved water retention, nutrient uptake, osmotic adjustment, and photosynthetic efficiency. Among the evaluated treatments, the combined application of Si (60 kg ha⁻¹) with SA (100 mg L–¹), GA₃ (50 mg L–¹), or MeJA (0.25 mM) proved most effective in mitigating drought induced damage. These treatments significantly enhanced leaf yield, herbage biomass, water productivity, photosynthetic rate, and biochemical traits such as proline, phenol, and flavonoid accumulation. Notably, plants treated with Si and either SA, GA₃, or MeJA at 75% field capacity (FC) outperformed control plants at optimal 100% FC, demonstrating the strong drought-alleviating effects of these biostimulants. |
| Year | 2025 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural Systems and Engineering (ASE) |
| Chairperson(s) | Datta, Avishek |
| Examination Committee(s) | Himanshu, Sushil Kumar;Salin, Krishna R. |
| Scholarship Donor(s) | TGIST/NSTDA;AIT Scholarship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2025 |