Biostimulants in Plant Science: A Global Perspective

Abstract

This review presents a comprehensive and systematic study of the field of plant biostimulants and considers the fundamental and innovative principles underlying this technology. The elucidation of the biological basis of biostimulant function is a prerequisite for the development of science-based biostimulant industry and sound regulations governing these compounds. The task of defining the biological basis of biostimulants as a class of compounds, however, is made more complex by the diverse sources of biostimulants present in the market, which include bacteria, fungi, seaweeds, higher plants, animals and humate-containing raw materials, and the wide diversity of industrial processes utilized in their preparation. To distinguish biostimulants from the existing legislative product categories we propose the following definition of a biostimulant as “a formulated product of biological origin that improves plant productivity as a consequence of the novel or emergent properties of the complex of constituents, and not as a sole consequence of the presence of known essential plant nutrients, plant growth regulators, or plant protective compounds.” The definition provided here is important as it emphasizes the principle that biological function can be positively modulated through application of molecules, or mixtures of molecules, for which an explicit mode of action has not been defined. Given the difficulty in determining a “mode of action” for a biostimulant, and recognizing the need for the market in biostimulants to attain legitimacy, we suggest that the focus of biostimulant research and validation should be upon proof of efficacy and safety and the determination of a broad mechanism of action, without a requirement for the determination of a specific mode of action. While there is a clear commercial imperative to rationalize biostimulants as a discrete class of products, there is also a compelling biological case for the science-based development of, and experimentation with biostimulants in the expectation that this may lead to the identification of novel biological molecules and phenomenon, pathways and processes, that would not have been discovered if the category of biostimulants did not exist, or was not considered legitimate.

Plant protection means used in organic farming throughout the European Union

“…The products discussed in this Perspective are not covered by the definition of a PPP. This topic is one of great interest with wide implications and is rather complex from a legal point of view . The line between PPPs and biostimulants of different types is not quite clear, as some chemicals, micro‐organisms and plant extracts have a wide and varied spectrum of action .…”

Biostimulants and possibilities of their usage in grassland

“…Yakhin, Lubyanov, Yakhin, and Brown () comparing definitions in light of scientific literature present a comprehensive view on the definitions of plant biostimulants used around the world. Over the years, the group of substances referred to as biostimulants has evolved, but recently, this term has been standardized.…”

“…General characteristics adopted by du Jardin () have been specified by other authors, who exclude fertilizers and pesticides, and emphasize the stimulating effect of biostimulants on plant metabolism, and on physiological, biochemical and hormonal processes. Many authors describe them as environment‐friendly substances, used in small or very small doses (Chojnacka (); Daniels, ; Halpern et al, ; Lovatt, ; Traon, Amat, Zotz, & Jardin, ; Yakhin et al, ).…”

Influence of Acacia dealbata Link bark extracts on the growth of Allium cepa L. plants under high salinity conditions

“…Plant chemical constituents can be used in biostimulant formulations for different agricultural purposes. According to Yakhin et al (2017), a biostimulant is defined as ‘a formulated product of biological origin that improves plant productivity as a consequence of the novel, or emergent properties of the complex of constituents, and not as a sole consequence of the presence of known essential plant nutrients, plant growth regulators, or plant protective compounds’. Biostimulants, mainly derived from natural raw materials, are generally a complex mixture of chemical constituents that are difficult to fully identify, and should be effective also at low doses .…”

“…Biostimulants, mainly derived from natural raw materials, are generally a complex mixture of chemical constituents that are difficult to fully identify, and should be effective also at low doses . Because of the multicomponent composition, the effect of biostimulants may be influenced by the geographical location, plant growing conditions, season, species, organ, and phenological stage, with their mode of action still unknown/unpredictable . Biostimulants include microbial inoculants, humic acids, fulvic acid hydrolysates of proteins, amino acids, or seaweed extracts, among others .…”