Bio Stimulants in Floriculture

Plant bio-stimulants refer to the natural or synthetic substances which are applied to seeds, plants and/or soil to cause changes in structural and vital processes in plant growth. The use of bio-stimulants generally increases nutrient uptake as well as nutrient use efficiency, thereby reducing the consumption of artificial fertilizers, which affect soil health tremendously.

Plant biostimulants are also widely used for organic production of different horticultural crops and also for adopting sustainable agricultural practices and in integrated cropping systems. Moreover, the use of biostimulants enhances different quality parameters like sugar content, colour, etc. 

Biotic stress reduces the crop yield and in severe situations may lead to complete crop loss. The use of bio-stimulants improves the plant's tolerance to various fungal, bacterial and viral infections. Thus, these are regarded as eco-friendly substances and considered as safe for consumption by human.  

Abiotic stress such as drought, salinity, and extreme temperatures affects the growth and productivity of plants and are responsible for huge crop losses globally. Bio-stimulants also act like auxins, gibberellins and cytokinins which optimize the plant's metabolism and growth and aids in mitigating the abiotic stresses, when applied exogenously.  

Categories of biostimulants  

1. Humic and fulvic acids: These are the natural dark-coloured elements of the soil organic matter, formed from the decomposition of plant, animal and microbial residues and also from the metabolic activity of soil microbes. Peat, volcanic soils, compost, vermicompost are the sources of humic substances. Humic substances boost soil fertility and improve the physical, physicochemical, chemical and biological properties of the soil.  

2. Protein hydrolysates and other nitrogen-containing compounds: Chemical and enzymatic protein hydrolysis of agro-industrial by-products yields amino-acids and peptides mixtures. Additional nitrogenous molecules include betaines, polyamines and non-protein amino acids. These compounds have beneficial effects as biostimulants on plant growth.  

3. Seaweed extracts: Seaweeds are green, brown and red marine macroalgae. It is composed of a mixture of complex polysaccharides, fatty acids, vitamins, phytohormones and mineral nutrients. At low concentrations, seaweeds are capable of increasing plant growth, improvement of flowering and yield.  Seaweeds also improve the nutritional content of the edible product as well as shelf life. 

4. Botanicals:Plants contain a high amount of various bioactive compounds which act as a main raw material for the production of valuable and useful bio-products. A botanical is a plant or plant part appreciated for its medicinal or therapeutic properties, flavour and/or scent. Botanicals are sold in the market in fresh as well as dried plant materials. Many plants like Pongamia seed extract, Lantana leaf extract, chrysanthemum leaf extract, Calotropis leaf extract, chilli fruit extract etc. are widely used by farmers against various pests with piercing-sucking and cutting-chewing type feeding behaviour. 

5. Chitosan and other biopolymers: Chitosan substances are natural plant defense activators derived from the deacetylation of chitin.They are commercially produced from seafood like crab shells, shrimp shells, squid pens from the food processing industry. The main application of chitosan is plant defense against pathogens, as it induces the production of protective molecules against pathogens. These substances also can induce resistance to abiotic stresses, including salt, drought and temperature stress. 

6. Beneficial Fungi: Mycorrhizal fungi are key for plant growth. They help in better root growth, nutrient absorption and provide a natural defense against root diseases and pests. The fungi help the plant to take up soil nutrients and water more efficiently. These fungi are widely used by urban vegetable and flower growers. 

7. Inorganic compounds: Inorganic compounds are minerals such as silica, selenium, cobalt and others which promote plant growth and tolerance to abiotic stress. These inorganic compounds influence pH, osmotic and redox homeostasis, hormone signalling and enzymes involved in stress response. Silicon is used profusely as biostimulants, it alleviates salt, drought and nutrient stress as well as stress associated with varied climatic conditions. 

Many commercial products containing mixtures of such substances and/or microorganisms are available in the market at affordable prices. Due to a lack of awareness or knowledge of the appropriate product to be used and from where to purchase, farmers end up losing their crops. The characterization of a biostimulant should be performed based on the plant responses.  Thus, an attempt is made to assemble the commercial biostimulants in this article. 

Different commercial biostimulants, their producing company and approximate cost 

Use of bio-stimulants in Floriculture 

Conclusion 

Regular use of chemicals in agriculture has declined the ecological base in addition to degradation of soil, water resources and quality of food. At this stage, the awareness of adopting organic farming is very much essential to develop a strong and compatible set of nutrient management through organic resources. The aim of these products besides supplying nutrition is to stimulate the metabolism of the plant. The biostimulant products offer a sustainable, environmentally-friendly means of enhancing crop productivity. The application of biostimulants in agriculture crop cultivation allows for higher levels of yields by reducing fertilizer usage and maintaining environmental health at the same time. 

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Author

Labdhi Dedhia  

¹Division of Floriculture and Medicinal Crops, ICAR-Indian Institute of Horticultural Research, Hesaraghatta, Bangalore-560089