Plant biostimulants are diverse substances and microorganisms used to enhance plant growth. The global market for biostimulants is projected to increase 12 % per year and reach over $2,200 million by 2018. Despite the growing use of biostimulants in agriculture, many in the scientific community consider biostimulants to be lacking peer-reviewed scientific evaluation. This article describes the emerging definitions of biostimulants and reviews the literature on five categories of biostimulants: i. microbial inoculants, ii. humic acids, iii. fulvic acids, iv. protein hydrolysates and amino acids, and v. seaweed extracts. The large number of publications cited for each category of biostimulants demonstrates that there is growing scientific evidence supporting the use of biostimulants as agricultural inputs on diverse plant species. The cited literature also reveals some commonalities in plant responses to different biostimulants, such as increased root growth, enhanced nutrient uptake, and stress tolerance.

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Agricultural uses of plant biostimulants

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.

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Biostimulants in Plant Science: A Global Perspective.

Protein hydrolysates as biostimulants in horticulture

Agricultural growing practices have been evolving towards organic, sustainable or environmental friendly systems The aim of modern agriculture is to reduce inputs without reducing the yield and quality These goals can be achieved by breeding programmes but would be species specific and time consuming The identification of organic molecules able to activate plant metabolism may allow an improvement in plant performance in a short period of time and in a cheaper way Biostimulants are plant extracts and contain a wide range of bioactive compounds that are mostly still unknown These products are usually able to improve the nutrient use efficiency of the plant and enhance tolerance to biotic and abiotic stresses In this review, the state of the art and future prospects for biostimulants are reported and discussed Moreover, particular attention has been paid to intensive agricultural systems such as horticultural and floricultural crops In vegetables, the application of biostimulants allowed a reduction

Biostimulants and crop responses: a review

Abiotic stresses strongly affect plant growth, development, and quality of production; final crop yield can be really compromised if stress occurs in plants’ most sensitive phenological phases. Additionally, the increase of crop stress tolerance through genetic improvements requires long breeding programmes and different cultivation environments for crop performance validation. Biostimulants have been proposed as agronomic tools to counteract abiotic stress. Indeed, these products containing bioactive molecules have a beneficial effect on plants and improve their capability to face adverse environmental conditions, acting on primary or secondary metabolism. Many companies are investing in new biostimulant products development and in the identification of the most effective bioactive molecules contained in different kinds of extracts, able to elicit specific plant responses against abiotic stresses. Most of these compounds are unknown and their characterization in term of composition is almost impossible; therefore, they could be classified on the basis of their role in plants. Biostimulants have been generally applied to high-value crops like fruits and vegetables; thus, in this review, we examine and summarise literature on their use on vegetable crops, focusing on their application to counteract the most common environmental stresses.

Biostimulants Application in Horticultural Crops under Abiotic Stress Conditions

The aim of the present study was to investigate the influence of spraying with Aminoplant on the yield of two spinach cultivars in the spring and autumn cultivations The experiment was carried out in 2008 and 2009 in the experimental station of the University of Agriculture in Krakow, Poland Three factors were taken into consideration: (1) cultivar: ‘Rembrandt F₁’ and ‘Spiros F₁’; (2) time of cultivation: spring and autumn; (3) dose of Aminoplant: control (without Aminoplant), 15 dm³ ha⁻¹ and 30 dm³ ha⁻¹ The spinach yield was dependent on the time of production and cultivar type, and ranged between 186-448 t ha⁻¹ Both cultivars yielded better in autumn cultivation Spraying with Aminoplant had no effect on spinach yield Dry matter content in spinach leaves was between 63-112 g 100 g⁻¹ Spinach grown in the autumn had a greater content of dry matter in comparison to the spring cultivation In 2009, ‘Rembrant F₁’ was characterized by greater dry matter content than ‘Spiros F₁’ Aminoplant in a dose of 30 dm³ ha⁻¹ lowered dry matter content in spinach leaves as compared to the control The nitrate content in spinach was differentiated (558-3506 mg NO₃ kg⁻¹ fm) and depended on the time of cultivation, the cultivar, and the Aminoplant dose

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The effect of cultivar type, time of cultivation, and biostimulant treatment on the yield of spinach (Spinacia oleracea L.)

Effects of LED supplemental lighting on yield and some quality parameters of lamb's lettuce grown in two winter cycles

Modifications in growing techniques can affect the yield and nutritional quality of various cultivated plants. Among them, the use of biostimulants is environmental friendly method of stimulating crop productivity, stress resistance, and affecting yield or chemical composition of the plants. The aim of the investigation was determining of the effect of biostimulant treatment on yield and its quality of carrot grown for summer harvest. The experiment was carried out in 2009-2011 in the experimental station of the University of Agriculture in Krakow, south Poland. Two experimental factors were taken into consideration: (1) cultivar: Nandrin F₁ and Napoli F₁ (2) dose of Aminoplant (foliar application): 1.5 and 3.0 dm³∙ha⁻¹ and control (without Aminoplant). Total and marketable yield, root length, its diameter, leaf mass and leaf : root mass ratio were assessed. The dry matter, soluble sugar, carotenoids and nitrate ions contents were analyzed as main determinants of carrot nutritional quality.Aminoplant influenced not only carrot productivity, but mainly chemical composition of the roots. The present results also suggest that carrot reaction to biostimulant treatment was depended on a cultivar more than on environmental conditions in particular growing seasons. The significant effect of Aminoplant in a dose of 1.5 dm³∙ha⁻¹ on the yield of roots and leaf rosette mass of ‘Nandrin F₁’ appeared only in the first year of the experiment. Spraying with Aminoplant in a dose of 3.0 dm³∙ha⁻¹ significantly increased the soluble sugars content in carrot roots of both cultivars but only in 2011. Dry matter content was also affected by biostimulant treatment mainly for ‘Napoli F1’, which showed the lowest dry matter content when sprayed with Aminoplant in a dose of 1.5 dm³∙ha⁻¹. In 2010 control plants contained the greater amount of carotenoids, while in next year roots of plants treated with Aminoplant in a dose of 3.0 dm³∙ha⁻¹ had more these compounds. The significant effect of Aminoplant on nitrates content in carrot roots was observed but were not repeatable in the experimental years, so different climatic conditions modified carrot reaction on biostimulant spraying.

https://www.degruyter.com/downloadpdf/j/vcrb.2012.77.issue--1/v10032-012-0014-1/v10032-012-0014-1.xml

The effect of cultivar and biostimulant treatment on the carrot yield and its quality.

Modifying folate and polyphenol concentrations in Lamb's lettuce by the use of LED supplemental lighting during cultivation in greenhouses

The results of a 3 year experiment with broccoli Lord F1 grown under field conditions in the spring growing cycle are presented. The aim of the study was to determine the effect of mineral nitrogen fertilization and foliar urea nutrition on the yield and content of some compounds in broccoli heads. Four different levels of mineral nitrogen (Nmin) in the soil were used: natural content (12-25.5 mg N/cubic dm), fertilization with half of the full rate supplemented to the level of 75 mg N/cubic dm, fertilization with the full rate divided into halves (75+75 mg N/cubic dm), and with the single full rate of N supplemented to the level of 150 mg N/cubic dm. In each Nmin treatment additionally two combinations were applied: without and with foliar application of 2 percent urea solution. According to the investigation, generally no significant effect of the mineral nitrogen rate on the biological and marketable yield of broccoli as well as on its quality was observed. The foliar urea application significantly lowered concentration of nitrates in broccoli heads in comparison with the plants not treated with urea. Additionally, irrespective of the year of study the foliar nutrition increased soluble sugar content in all Nmin treatments. Moreover in each year of the experiment the increase of ascorbic acid content in broccoli heads treated with urea was showed

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Renata Wojciechowska

Papers

The effect of cultivar type, time of cultivation, and biostimulant treatment on the yield of spinach (Spinacia oleracea L.)

Effects of LED supplemental lighting on yield and some quality parameters of lamb's lettuce grown in two winter cycles

The effect of cultivar and biostimulant treatment on the carrot yield and its quality.

Modifying folate and polyphenol concentrations in Lamb's lettuce by the use of LED supplemental lighting during cultivation in greenhouses

Broccoli yield and its quality in spring growing cycle as dependent on nitrogen fertilization.