An Endophytic Fungi-Based Biostimulant Modulates Volatile and Non-Volatile Secondary Metabolites and Yield of Greenhouse Basil (Ocimum basilicum L.) through Variable Mechanisms Dependent on Salinity Stress Level

Abstract

Salinity in water and soil is one of the major environmental factors limiting the productivity of agronomic and horticultural crops. In basil (Ocimum basilicum L., Lamiaceae) and other Ocimum species, information on the plant response to mild salinity levels, often induced by the irrigation or fertigation systems, is scarce. In the present work, we tested the effectiveness of a microbial-based biostimulant containing two strains of arbuscular mycorrhiza fungi (AMF) and Trichoderma koningii in sustaining greenhouse basil yield traits, subjected to two mild salinity stresses (25 mM [low] and 50 mM [high] modulated by augmenting the fertigation osmotic potential with NaCl) compared to a non-stressed control. The impact of salinity stress was further appraised in terms of plant physiology, morphological ontogenesis and composition in polyphenols and volatile organic compounds (VOC). As expected, increasing the salinity of the solution strongly depressed the plant yield, nutrient uptake and concentration, reduced photosynthetic activity and leaf water potential, increased the Na and Cl and induced the accumulation of polyphenols. In addition, it decreased the concentration of Eucalyptol and β-Linalool, two of its main essential oil constituents. Irrespective of the salinity stress level, the multispecies inoculum strongly benefited plant growth, leaf number and area, and the accumulation of Ca, Mg, B, p-coumaric and chicoric acids, while it reduced nitrate and Cl concentrations in the shoots and affected the concentration of some minor VOC constituents. The benefits derived from the inoculum in term of yield and quality harnessed different mechanisms depending on the degree of stress. under low-stress conditions, the inoculum directly stimulated the photosynthetic activity after an increase of the Fe and Mn availability for the plants and induced the accumulation of caffeic and rosmarinic acids. under high stress conditions, the inoculum mostly acted directly on the sequestration of Na and the increase of P availability for the plant, moreover it stimulated the accumulation of polyphenols, especially of ferulic and chicoric acids and quercetin-rutinoside in the shoots. Notably, the inoculum did not affect the VOC composition, thus suggesting that its activity did not interact with the essential oil biosynthesis. These results clearly indicate that beneficial inocula constitute a valuable tool for sustaining yield and improving or sustaining quality under suboptimal water quality conditions imposing low salinity stress on horticultural crops.

Editorial: Arbuscular Mycorrhizal Fungi: The Bridge Between Plants, Soils, and Humans

“…Along similar lines, mycorrhizal benefits were also elaborated on the medicinal plant Eclipta prostrata ( Duc et al ) subjected to salinity stress, which seem to have been coupled with modulation of the polyphenol production. Thus, the present results generally confirm previous findings on the ability of the AM fungi to modulate secondary metabolism (Zeng et al, 2013 ; Lazzara et al, 2017 ; Saia et al, 2019 ) of a range of medicinal and other plants, despite the remaining uncertainty in the mycorrhizal effects on the volatile compounds composition (Saia et al, 2021 ).…”

The Effects of the Microbial Biostimulants Approved by EU Regulation 2019/1009 on Yield and Quality of Vegetable Crops

“…Therefore, the plant ionome was more affected by the plant species than by inoculation with AMF [ 36 ]. Basil inoculation with Funneliformis mosseae and Rhizoglomus irregulare (homotypic synonyms: Glomus mosseae and Glomus irregulare , respectively) increased Fe and Mn content [ 37 ], decreased the accumulation of the antinutrient nitrate and improved yield [ 38 ]. In basil plants under salinity, the same AMF enhanced Na compartmentalization and P availability [ 37 ].…”

“…Basil inoculation with Funneliformis mosseae and Rhizoglomus irregulare (homotypic synonyms: Glomus mosseae and Glomus irregulare , respectively) increased Fe and Mn content [ 37 ], decreased the accumulation of the antinutrient nitrate and improved yield [ 38 ]. In basil plants under salinity, the same AMF enhanced Na compartmentalization and P availability [ 37 ]. Glomus etunicatum , Glomus fasciculatum (homotypic synonyms: Claroideoglomus etunicatum and Rhizophagus fasciculatus , respectively) and Glomus intraradices increased basil root dry weight, leaf area, plant height, number of lateral branches and mineral content (e.g., N, P, K, Ca, Fe, Cu and Mn) [ 39 ].…”

“…Funnelliformis mosseae and R. irregulare basil inoculation enhanced phenols, and in particular caffeic and rosmarinic acids and photosynthesis [ 37 ], in addition to chlorophylls [ 38 ] under non-saline conditions. However, in basil plants under salinity, the same AMF induced the accumulation of polyphenols (i.e., ferulic and chicoric acids and quercetin-rutinoside) [ 37 ].…”

“…Funnelliformis mosseae and R. irregulare basil inoculation enhanced phenols, and in particular caffeic and rosmarinic acids and photosynthesis [ 37 ], in addition to chlorophylls [ 38 ] under non-saline conditions. However, in basil plants under salinity, the same AMF induced the accumulation of polyphenols (i.e., ferulic and chicoric acids and quercetin-rutinoside) [ 37 ]. G. etunicatum and G. intraradices , but in particular G. fasciculatum , increased basil essential oils (particularly linalool) [ 39 ]; the same G. fasciculatum increased also chicoric acid and a caffeic acid derivative in basil [ 40 ].…”