Vesicular arbuscular mycorrhizal influence on Sutherland frutescens secondary metabolites, performance and saline stress alleviation.

Abstract

The global population is continuously increasing, leading to a corresponding rise in demand for valuable medicinal plants, such as cancer bush (Sutherlandia frutescens L. (Br.)). Nevertheless, arable land is scanty, while the available land has high concentrations of salt ions, NaCl and CaCl2. Alternative sustainable solutions to manage the one are necessary to safeguard the land for future use, while maintaining food security demands. Such solutions include the use of Vesicular Arbuscular Mycorrhiza (VAM) fungi, which haves become a hot topic and efficient solution to abiotic stress incidences. The objectives of the study were to: (1) determine whether VAM fungi will improve growth and yield of S. frutescens and alleviate salinity stress (2) evaluate whether biosynthesis and accumulation of phytochemicals of S. frutescens will be influenced using VAM fungi in reducing salinity. A shade net and microplot experiments were conducted at the University of Mpumalanga in 2024. The two independent experiments were carried out as a 4x4 factorial arrangement laid out in a randomised complete block design (RCBD) with four replications. The treatments comprised of different levels of VAM (0, 10, 20, and 30 g) and chloride salinity (0, 0.25, 0.5, and 0.75 dS m⁻¹), formulated as a 3:1 mixture of sodium chloride (NaCl) and calcium chloride (CaCl₂). The data collected included growth, physiological and plant biomass. The results in both experiments have shown that treatments had a significant effect (p < 0.05) on plant growth variables. Among the measured plant variables in experiment 1, VAM fungi had a significant impact (p < 0.05) on stem diameter, chlorophyll content, and the number of branches, accounting for 94.21%, 96.76%, and 98.11% of the total treatment variation (TTV). Similarly, in experiment 2, VAM fungi had a significant effect (p < 0.05) on chlorophyll, stem diameter, and plant fresh weight, contributing to a TTV of 91.99%, 98.12%, and 91.09%. The results revealed that, the v applied VAM fungi in Experiment 1, had relative positive effect on stem diameter, chlorophyll, and plant fresh weight compared to the control with a relative impact (RI) of 204.55 to 588.74%, 101.61 to 314.6% and 1350.96 to 5253.65%, respectively. While in experiment 2, VAM fungi increased chlorophyll content, stem diameter, and plant fresh weight with a RI of 85.59 to 278.88%, 307.34 to 890.40%, and 65.40 to 207.87%, respectively. The interactive application of salt and VAM treatment exhibited a notable impact on pH, among the measured variables in Experiment 1 only, with a TTV of 30.37%. The interactive application (0*75dS m⁻¹) resulted in the increase of soil pH by 18%. Vesicular-Arbuscular Mycorrhizal fungi, salt treatments, the interaction of salt and VAM fungi had a significant effect on the TPC in experiment 1, contributing 30.01%, 40.30%, and 29.25% of the TTV, while in Experiment 2, treatments had a substantial effect on TPC with a TTV of 98.43, 0.33, and 0.47%, respectively. Similarly, VAM fungi, salt treatments, and the interaction of salt and VAM fungi had a significant effect (p<0.05) on the TFC in Experiments 1 and 2, contributing to the TTV of 98.43%, 1.21%, and 0.35% and the TTV of 99.7%, 0.02% and 0.27%, respectively. The results demonstrated that, VAM boosts plant resilience to saline stress, enhances physiological traits, and affects the accumulation of secondary metabolites. The interaction of VAM and salinity treatments influenced TPC in experiment 2 only. The TPC was increased by the interaction with relative impact of 15.37% to 72.05%. Similar results were observed for TFC, where in experiment 1 and 2, the interaction increased the TFC by 0.07 to 0.57% in Experiment 1, whereas in experiment 2, TFC was reduced by 3.71% to 4.47%. Thus, the integration of VAM fungi in the cultivation of S. frutescens is a viable approach to augmenting plant development and resilience in saline stress conditions. It is advisable to conduct additional studies to enhance the techniques of VAM application aimed at optimising plant productivity and the biosynthesis of metabolites.