Protective Effects of Salicylic Acid and Calcium Chloride on Sage Plants (Salvia officinalis L. and Salviaelegans Vahl) under High-Temperature Stress

Abstract

High-temperature stress is a major risk to fresh-market Salvia production, and heat intolerance is a major constraint in sage cultivation, particularly during the hot summer season. Previously, we investigated heat tolerance in five common-market cultivars of sage plants using leaf relative injury (RI) values and found that S. elegans Vahl (SE) and S. officinalis L. (SO) were the most and least heat-tolerant species, respectively. The exogenous applications of salicylic acid (SA) and calcium chloride (CaCl2) to alleviate heat stress in various species have been extensively studied, but reports of the effects of SA and CaCl2 treatments on the heat tolerance of sage plants are scarce. The objective of this study was to investigate how SA and CaCl2 affect the physiology and morphology of SE and SO plants under high-temperature conditions. Potted plants were pretreated with SA (0, 100, 200, 400, and 800 μM) and CaCl2 (0, 5, 10, and 15 mM), alone and combined, exposed to 55 °C and 80% humidity for 30 min, then placed in an environment-controlled chamber at 30°C for three days and evaluated for changes in phenotypic appearance, RI, spectral reflectance, and chlorophyll fluorescence indices at different time intervals. Plants watered without chemical solutions were used as controls. Our results show that the growth of SO plants pretreated with SA and CaCl2 was more robust, compared with control plants, which were considerably affected by heat stress, resulting in brown, withered leaves and defoliation. The effects of the combined applications of SA (100 μM) and CaCl2 (5 mM) to SO plants were superior to control plants in increasing values of soil-plant analysis development (SPAD), normalized difference vegetation index (NDVI), and the maximal quantum yield of photosystemII photochemistry (Fv/Fm), while reducing RI%. Furthermore, SO plants exhibited higher SPAD and Fv/Fm values and lower RI% than SE plants in combined treatments at all time intervals after heat stress, implying that different genotypes displayed variations in their SPAD, Fv/Fm, and RI%. Thus, a combined treatment of 100 μM of SA and 5 mM of CaCl2 is effective and beneficial to plant appearance and ability to ameliorate heat stress. These indices can be used as indicators to characterize the physiology of these plants and applied on a commercial scale for informing the development of rapid and precise management practices on bedded sage plants grown in plant factories to achieve maximum market benefit.

Antagonist Temperature Variation Affects the Photosynthetic Parameters and Secondary Metabolites of Ocimum basilicum L. and Salvia officinalis L.

“…Only a few studies can be found in the literature. Namely, a reduction of the total chlorophyll content was observed, from 50.93 to 31.92 after 3 days after exposure to high temperature stress, 55 °C and 80% humidity for 30 min [ 30 ].…”

“…The plants most susceptible to climate change are expected to be the species with low thermotolerance [ 1 , 23 , 27 ]. Basil ( Ocimum basilicum L.) and sage ( Salvia officinalis ) ( Labiatae / Lamiaceae family) are popular culinary and medicinal herbs and are moderately temperature-tolerant plants grown in temperate regions [ 28 , 29 , 30 ].…”

“…The effects of heat stress on plants can be defined as a decrease in photosynthesis, Rubisco activity, and the synthesis of reactive oxygen species (ROS) in analyzed plants [ 26 , 30 , 31 ]. The reduction of photosynthesis in plants subjected to heat stress is linked with a decrease in photosystem centers II (PSII) activities and photosynthetic electron transport activity [ 31 , 32 ].…”

Influence of Climate-Related Environmental Stresses on Economically Important Essential Oils of Mediterranean Salvia sp.

“…Salicylic acid and calcium are recognized as signaling molecules in plants’ responses to oxidative stress induced by different environmental factors ( Laanemets et al, 2013 ; Janda and Ruelland, 2015 ). Growth inhibition can be effectively alleviated by external application of salicylic acid (SA) or calcium (Ca 2+ ) alone or in combination, as reported by Lin et al (2021) . They recorded an increase in new leaves formation under high-temperature stress when plants were treated with SA and Ca 2+ ( Figure 3 ).…”

“…In Mediterranean areas, the crop is subjected to summer drought stress, high temperature, soil salinity, and enhanced ozone levels ( Pellegrini et al, 2018 ), which affect its composition and potential use. An increase in global temperatures is imposing additional stress on sage affecting essential oil composition and affecting sage cultivation and production due to leaf etiolation, wilting, and reduced photosynthetic capacity of plants ( Lin et al, 2021 ). Under hot and arid conditions, accumulation of thujone has been recorded as a response to heat and water stress, while under optimal conditions camphor is mainly accumulated ( Nevkrytaya et al, 2021 ).…”