Willow (Salix babylonica) Extracts Can Act as Biostimulants for Enhancing Salinity Tolerance of Maize Grown in Soilless Culture

Abstract

Salinity negatively affects agricultural production by reducing crop growth and yield. Botanical biostimulants can be used as innovative and sustainable tools to cope with abiotic stress. In this study, salicylic acid (SA) (25 µM) and willow leaf (WL) (0.1 and 0.2%) and bark (WB) (0.1 and 0.2%) extracts were applied as plant-based biostimulants to hydroponically grown maize in the absence and presence of salinity stress (60 mM NaCl). The hormone-like activity and mineral composition of willow extracts were analyzed, and the effects of willow extracts on growth parameters, chlorophyll content, antioxidative enzyme activities, protein levels and mineral nutrient concentrations of maize plants were measured. Within the tested biostimulant applications, 0.2% WB, 0.1% WL and 0.2% WL gave the most promising results, considering the stress alleviating effects. The shoot biomass was increased up to 50% with 0.1% WL treatment and Na+ uptake was reduced with biostimulant applications under saline conditions. Under stress, the protein concentrations of maize leaves were enhanced by 50% and 80% with high doses of WB and WL applications, respectively. Results indicate that willow tree prunings can be valuable bio-economy resources, and aqueous extracts prepared from their leaves and barks can be used as effective and eco-friendly biostimulants.

Advances in Roles of Salicylic Acid in Plant Tolerance Responses to Biotic and Abiotic Stresses

“…However, the exact mechanisms in this process are not yet fully understood [78]. In a word, recent studies made remarkable advances in SA's roles in plant tolerance responses to both biotic and abiotic stresses [47,48,71,72,82,84,[86][87][88][118][119][120][121][122][123], and in both physiological [124][125][126] and molecular perspectives [127][128][129][130]. For example, Yao et al proposed a high air humidity-triggered significant suppression of SA accumulation and signaling associated with compromised immunity of Arabidopsis plants [130], which indicates the value of research concerning SA's roles in multiple stresses confronted by plants.…”

“…heat, cold citrus plants Involvement in fruits' heat-induced cross-adaptation to chilling [39] heat wheat Protection against heat stress; reduction of oxidative stress; increment of antioxidant enzyme activities; improvement of photosynthesis and growth [42] salt cereal crops Enhancement of salt tolerance [43] salt, drought chilli Significant effects against salt stress; elicitation of proline accumulation for the development NaCl-induced drought stress tolerance [44] salt maize Alleviation of salinity; significant enhancement of grain yield [47] salt maize Enhancement of salinity tolerance [48] heavy metals general plants Induction of acclimatization impacts; improvement of tolerance against heavy metal stress [49] heavy metals common bean Improvement of growth traits and photosynthetic indexes; enhancement of antioxidant enzyme activities and proline accumulation [50] heavy metals general plants Improvement of stress tolerance; modulation of ROS detoxification machinery to protect plants against HM-induced oxidative stress; modulation of non-enzymatic antioxidant metabolite levels [51] drought…”

“…In terms of specific effects, SA can promote the growth and development of plant roots, enhance plant stress resistance, increase chlorophyll content and photosynthetic efficiency in leaves, and reduce transpiration and water loss [48,83,98]. Additionally, SA can promote plant physiological metabolism [36,94,96,102,111,117], thus increasing plant disease resistance and improving salt and drought tolerance.…”

“…It is generally held that SA plays vital roles in plant stress tolerance. SA's main roles in plant tolerance to stresses can be summarized as following: the activation of plant defense mechanisms [2,[11][12][13][14], the improvement of photosynthesis [15][16][17][18][19][20][21][22], the regulation of plant normal growth and development [8,19,[23][24][25][26][27][28][29][30], and the enhancement of plant tolerance to drought [9,11,[31][32][33][34][35][36], cold [37][38][39], heat [36,[39][40][41][42], salt [43][44][45][46][47][48], and heavy metal stresses [49][50][51]…”

“…New research has shown that SA plays multiple roles in enhancing plant stress resistances [32,38,43,73,77]. Such roles of SA can be categorized into the following aspects: immune response [13,25,[78][79][80], antioxidative defense [11,20,[53][54][55][56][57][58][59], salt tolerance [43][44][45]47,48,[81][82][83][84], and drought tolerance [2,11,[32][33][34][35][36]71,[85][86][87].…”