Rate and Timing of Application of Biostimulant Substances to Enhance Fruit Tree Tolerance toward Environmental Stresses and Fruit Quality

Abstract

Biostimulants represent an important category of agricultural inputs characterized by multiple functions. They are used to assist crop growth, yield and to enhance the final quality of produces. Their classification is generally based on claims (i.e., which services they provide to the crop), even though their biological effects are often species-dependent and highly influenced by external factors (i.e., the growing conditions). This review provides a survey of the available scientific literature on the use of biostimulant substances in fruit production, with the specific aim to clarify their predominant mode and time of application. An extremely varied scenario emerged where foliar treatments are common for seaweed extracts, humic and fulvic acids, and where protein hydrolysates and silicon are applied both to the soil (drench) or sprayed to the canopy. Dosages were difficult to compare between the considered studies given the wide range of tested products and the uncertainty in their actual composition. Regarding the number of applications, biostimulants are generally applied following a calendar-approach, covering most of the growing season. When their use is intended to enhance crop tolerance toward environmental stresses, biostimulants are mainly applied before the stressful event to prime plant physiological defenses. Further studies based on multiple-year research projects and standard methodological protocols are urgently needed to verify a clear compliance with biostimulant claims and to evaluate their cost-effectiveness for the fruit production sector.

Foliar Application of Nano-Silicon Improves the Physiological and Biochemical Characteristics of ‘Kalamata’ Olive Subjected to Deficit Irrigation in a Semi-Arid Climate

“…The application of nano-silicon (nSi) has been suggested to enhance plant tolerance to drought stress by reducing the production of reactive oxygen species (ROS) in barley, wheat, faba bean, feverfew, strawberry, Mahaleb cherry, and mango [34,[48][49][50][51][52][53][54]. The primary mechanisms of Si-mediated abiotic stress reduction include plant antioxidant system activation, co-precipitation and immobilization of toxic metal ions in the growth medium, and metal absorption and separation within the plants [55][56][57][58][59][60][61][62][63][64][65][66][67][68].…”

Phytohormone-Based Biostimulants as an Alternative Mitigating Strategy for Horticultural Plants Grown Under Adverse Multi-Stress Conditions: Common South African Stress Factors

“…This lack of clarity is undoubtedly due to the nature of these products, whose composition frequently precludes detailed analysis and quantification of all components. Furthermore, the composition of the same product category can vary significantly depending on the material used and the manufacturing conditions (Andreotti et al, 2022).…”

Plant-Based Biostimulants for Seeds in the Context of Circular Economy and Sustainability

“…Biostimulant activity is influenced by various factors such as plant genotype, growth conditions, dosage, and application time [45]. A recent review [49] emphasizes the significance of the PBs application method. Some of the important factors to be considered while choosing the relevant mode of action are: (i) the uptake of biostimulants after application, (ii) knowledge regarding the bioactive compounds, and (iii) the absorption capacity of the target organ.…”