A Natural Bio-Stimulant Consisting of a Mixture of Fish Protein Hydrolysates and Kelp Extract Enhances the Physiological, Biochemical and Growth Responses of Spinach under Different Water Levels

Abstract

Spinach (Spinacia oleracea L.) is a highly nutritious, desirable green leafy vegetable, which is less tolerant to drought. This study was conducted to establish the impact of a natural bio-stimulant consisting of a mixture of fish protein hydrolysates and kelp extract (trade name, Xcell Boost) on the physiological and biochemical responses as well as vegetative growth of spinach (Spinacia oleracea L.) under different water levels (100% (full irrigation), 50% (mild drought stress) and 30% (severe drought stress) water holding capacity). Bio-stimulant application at any strength (single, BX1 or double, BX2) had no effect on the photochemical reactions. The application of bio-stimulant at double strength concentration (BX2) increased the chlorophyll and carotenoid contents, as well as the activities of antioxidative enzymes, ascorbate peroxidase (APX) and guaiacol peroxidase (GPX), under drought stress. Application at single strength (BX1) increased the normalised difference vegetation index (NDVI), stomatal conductance, accumulation of osmoprotectants (proline and total soluble sugars) and reduced electrolyte leakage under drought stress. Furthermore, bio-stimulant applications at either concentration induced remarkable increases in plant height, leaf area, stem dry weight, root length and root moisture. Under BX2, APX and stomatal conductance positively correlated with stem dry weight, while root length positively correlated with total chlorophyll content. These results show that Xcell Boost is a highly advantageous bio-stimulant for increasing the tolerance of spinach to drought stress, which can most likely benefit other crops grown in semi-arid and arid areas.

Agroindustrial By-Products as a Source of Biostimulants Enhancing Responses to Abiotic Stress of Horticultural Crops

“…Many studies (e.g., [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 ]) have reported beneficial effects of the application of protein hydrolysate biostimulants on crop growth, yield and product quality (e.g., in tomato, spinach, lettuce, celery, melon, chickpea, maize or beans). For example, Testani et al [ 79 ] in Capsicum annuum and Choi et al [ 80 ] in Solanum lycopersicum and Lactuca sativa observed that protein hydrolysates increased nutrient uptake, especially nitrogen, by acting directly on enzymes of nitrogen and carbon metabolism, such as glutamine synthetase, glutamate synthase, nitrate reductase, nitrite reductase, malate and isocitrate dehydrogenases and citrate synthase; these results are in agreement with those obtained in Zea mays plants [ 81 ].…”

“…Chemical or enzymatic hydrolysis of proteins produces amino acids and peptide mixtures from agroindustrial by-products, which can be of vegetable origin (crop by-products: seeds, husks, biomass and fruits) [ 34 , 57 , 84 , 86 , 89 , 90 ] or derived from animals, e.g., blood, feathers, viscera, bones, skins and other waste products [ 35 , 76 , 81 , 91 , 92 , 93 , 94 ]. These mixtures contain bioactive compounds that function as plant biostimulants, improving growth and enhancing abiotic stress tolerance.…”

“…Casadesus et al [ 97 ] obtained promising results in tomato plants under temperature stress, using a biostimulant based on hydrolysed animal protein, which led to increasing salicylic acid contents and favoured root growth of the treated plants. Furthermore, Liatile et al [ 76 ] found that applying fish protein hydrolysates to Spinacia oleracea plants improved growth and increased chlorophyll and carotenoid content under drought conditions.…”

Biostimulant Properties of Protein Hydrolysates: Recent Advances and Future Challenges

“…After drought imposition, (plant-derived PH) GHI_16_VHL-primed Capsicum annuum L. plants recovered faster probably due to the higher leaf osmolyte accumulation during drought [146]. Xcell Boost (a mixture of fish protein hydrolysates and Kelp extract (Ecklonia maxima)) treatment also increased the accumulation of osmoprotectants (proline and total soluble sugars) in spinach under drought stress [147].…”

Effects of Protein Hydrolysate Derived from Anchovy By-Product on Plant Growth of Primrose and Root System Architecture Analysis with Machine Learning

“…FPH can be applied to plants as drenching or foliar spray. FPH is proven to improve plant performance, including yield and quality in lettuce [14,15], spinach [16,17], wheat [18], and melon [19]. Moreover, FPH has been demonstrated to enhance plant nutrient utilization and root development [20].…”