April 24, 2023 at 3:20 pm | Updated April 24, 2023 at 3:20 pm | 7 min read
- Biostimulants use is becoming common for agricultural and horticultural crops.
- The various categories of biostimulants improve fruit quality by enhancing appearance, size, shape, sensory, and nutritional attributes.
- The effect of biostimulants on fruit quality depends on the composition, dose, and application method. Moreover, plant species, health, and the environment also produce differences in biostimulant action between years, farms, and fruits.
Biostimulants are one of the agtech innovations to achieve a sustainable increase in food production while reducing the use of agrochemicals. Biostimulant use has become a standard practice since it enhances yield and quality and is environmentally friendly, non-polluting, and without adverse effects on diversity. Most information on biostimulants focuses on their ability to improve plant productivity or stress tolerance. However, little is known about how biostimulants enhance fruit quality, as research and practice in this application of biostimulants have just begun. You will learn more about this new exciting agtech development in this article.
What are Biostimulants?
Biostimulants contain natural-origin compounds or microbes to stimulate plant processes to improve nutrient use efficiency and tolerance to abiotic and biotic stresses. Nutrient use efficiency could mean better nutrient absorption from the soil, transportation, storage, and use in plant and root growth.
They are added to the soil or used as foliar sprays. Biostimulant use can increase seed germination, seedling development, and enhanced flowering, fruit formation, yield, and fruit quality, even though they are not fertilizers.
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Biostimulants increase crop growth and yield by increasing plant hormones or stimulating soil microbial and enzyme activity. Similarly, biostimulants support and boost the plant’s metabolic processes and reduce stress effects.
The various beneficial effects of biostimulants on plant growth, yield, and quality are depicted in Figure 1. However, each biostimulant will have a different pathway and impact.
Categories of Biostimulants
Currently, six categories of biostimulants are recognized based on their origin and composition and are discussed below.
Beneficial fungi and bacteria improve nutrient status, productivity, and stress resistance. They also enhance soil biodiversity and mitigate soil degradation caused by agrochemicals.
The fungi used can be arbuscular, orchid, ericoid, and ectomycorrhizal. Though arbuscular mycorrhizal fungi (AMF) account for 90 percent of the fungal symbiosis with plants, their use in biostimulants is challenged because they aren’t easy to propagate on a large scale, and more information is needed on host-fungus relationships. Trichoderma spp, which are endophytes, are easier to propagate in vitro and are used more as biostimulants. Other fungal species used are Piriformospora, Fusarium spp., Aspergillus spp., Penicillium spp., Rhizophagus, and Funneliformis.
The bacteria are plant growth-promoting rhizobacteria (PGPRs) and bacteria. They can be mutualistic endosymbionts like Rhizobium or mutualistic PGPRs. The PGPRs are used most often as biostimulants.
Humic and fulvic acids are derived from the decomposition of soil organic matter. They are further grouped based on their activity- humic acids soluble in a basic substrate, fulvic acid soluble in acid and alkali media, and humins that can’t be extracted from soils.
Seaweed extracts and botanicals are plant-based products. Seaweed extracts are the most common biostimulants used. Liquid seaweed extracts were available from the 1950s and were commonly used before agrochemicals were introduced. They are now again widely used for horticultural and agricultural crops. Seaweed extracts contain several beneficial compounds found only in seaweeds, like plant hormones, sterols, polyamines, and polysaccharides. Ascophyllum nodosum is the most common seaweed for extracts; other species used are Ecklonia maxima, Jania rubens, Ulva lactuca, and Pterocladia capillacea.
Botanicals are derived from plants, and though more commonly used as plant protection compounds, their use for plant stimulation has started.
Protein-based products can be hydrolysates and N-containing compounds. Hydrolysates are a mixture of amino acids and peptides from plants or animals produced through enzymatic, chemical, and thermal hydrolysis processes.
Biopolymers like chitosan are used as biostimulants based on the size of their molecules. Chitosan is made from chitin found in the shells of crustaceans, like crabs and shrimps.
Inorganic compounds, such as aluminum, cobalt, selenium, and silicon, are found in the soil or plants. They are necessary for various physiological processes like growth, plant resistance, stress response, etc.
Figure 1: “Schematic representation of biostimulants use on sweet cherry tree, Afonso et al. 2022. (Image credits: Agronomy 2022, 12(3), 659; https://doi.org/10.3390/agronomy12030659)
Biostimulant Effect on Fruit Quality
The most common biostimulant to improve fruit quality is seaweed extracts from Ascophyllum nodosum and Ecklonia maxima. Next, protein hydrolysates enhance fruit and vegetable quality by improving plant nutrition.
The effect of biostimulants varies based on their composition, dose, and mode of application. The processing method of the biostimulants and the plant phenological stage, health and nutritional status, species, and environmental conditions will also moderately affect biostimulant action. So growers should test products before they use them and evaluate the biostimulants for the targeted goal, fruit quality, stress tolerance, or productivity.
Biostimulants’ effect on fruit quality can vary. They can improve sensory such as fruit size, shape, appearance, and taste. Or plant biostimulants can also augment the nutritional value of fruits and increase shelf life.
Fruit size, shape, color, and taste
Seaweed extracts, inorganic compounds, chitosan, and humic acids can improve fruit shape, size, color, and sensory attributes like taste.
- Extract from Ulva lactuca, Pterocladia capillacea, and Jania rubens increased fruit length and diameter in hot pepper. Extracts from nodosum also increased soluble sugars in eggplants.
- Inorganic compounds made of carboxylic acids increased fruit width, length, and thickness in apricots.
- Protein and N-based biostimulants are known to improve fruit color. For example, the capsicum variety Palermo’s fruit color was enhanced due to increased carotenoids by applying a commercial biostimulant composed of amino acids and vitamins as a spray for leaves and fruits.
- Humic and fulvic acids also improved fruit length in apricots. Humic acids as foliar and soil sprays also increased total soluble solids, and the ratio of BRIX and acidity improved the taste of several fruits.
- Chitosan improved fruit size and color in strawberries. Chitosan also improved the soluble sugar content in nectarine.
- mosseae, an AMF, boosts soluble sugars in honey melon (Cucumis melo).
Fruit Quality Meters like those produced by Felix Instruments Applied Food Science can estimate the chemical quality parameters like soluble sugars content, dry matter, pH, acidity, and color to evaluate the efficacy of biostimulant use.
Fruits like cherries are prone to peel cracking for various reasons, like genotype, soil type, rainfall volume, and intensity. The cracking can lead to harvest losses, which is unacceptable to consumers. Seaweed extract prepared from Ascophyllum nodosum reduces peel cracking and increases fruit wax production in cherries. A thicker fruit skin wax reduces moisture loss, protects the fruits from microbial infestation, and maintains firmness.
Positive results were obtained in retaining the firmness of fruits by using biopolymers, chitosan, humic and fulvic acid, and inorganic compounds.
- Biopolymers, humic and fulvic acids, and inorganic compounds improved fruit firmness in apricots, but yearly variations can be expected.
- Chitosan enhanced firmness in strawberries, raspberries, and sweet cherries when applied as a preharvest application.
Figure 2: “Enhancement of total anthocyanins, carotenoids, total flavonoids, phenolics contents, and antioxidant activity of fresh strawberry cv. Festival by the treatment of chitosan,” Rahman et al. 2018. (Image credit: https://doi.org/10.1371/journal.pone.0203769)
Nutraceuticals are compounds found in plants that are healthy for people. Consumers are increasingly looking for healthy fresh produce, and growers can boost sales chances and pricing by increasing these compounds in their crops. Several of the biostimulant groups enhance the nutritional value of vegetables and fruits, as discussed below:
- Protein-based biostimulants derived from chicken feathers, given as 5 percent foliar spray and 20 percent fertigation, increased the concentrations of amino acids, proteins, reducing sugars, phenolics, and flavonoids in ripe banana fruits.
- Seaweed extracts prepared from nodosum increased the total antioxidants in eggplants’ pulp, skin, and anthocyanin in peels. However, responses to biostimulants varied among cultivars of eggplants and year of cultivation.
- Botanicals like biostimulants made from alfalfa and grapes increased ascorbic acid and antioxidant activity in green peppers and capsaicin in red fruits.
- Humic acids increased carotenoids in sweet pepper.
- Chitosan improved the accumulation of phenolic compounds in many plants. It is an indirect effect of chitosan increasing levels of defense enzymes like phenylalanine ammonia-lyase that are also involved in synthesizing phenols. Also, chitosan significantly increased carotenoids, flavonoids, anthocyanins, and phenolics by 2.6 folds in strawberry fruits, see Figure 2.
- AMF ( mosseae) induces enhanced antioxidants in honey melon (Cucumis melo) grown in greenhouses.
Since postharvest treatment influences fruit quality and shelf life, biostimulants application can also help in this stage. For example, chitosan as a postharvest application can prevent decay during storage by delaying microbial infection and thus extend fruit shelf-life.
Meeting Consumer Satisfaction
The quality attributes that consumers look for in fruits are changing. Traditionally they considered physical parameters like appearance, size, color, firmness, signs of damage, and weight, and chemical characteristics like sweetness, taste, and maturity. Consumers now also look for better nutritional value in their food, defined by compounds like phenols, antioxidants, carotenoids, vitamins, etc. Biostimulants can help growers meet quality demands by consumers without using chemicals and make food safer for the public, another growing concern nowadays.
Afonso, S., Oliveira, I., Meyer, A. S., & Gonçalves, B. (2022). Biostimulants to improved tree physiology and fruit quality: A review with special focus on Sweet Cherry. Agronomy, 12(3), 659. https://doi.org/10.3390/agronomy12030659
Ali, M., Cheng, Z., Hayat et al. (2019). Foliar spraying of aqueous garlic bulb extract stimulates growth and antioxidant enzyme activity in eggplant (Solanum melongena L.). J. Integr. Agric., 18, 1001–1013.
Bhupenchandra, I., Devi, S., Basumatary, A., et al. (2020). Biostimulants: Potential and Prospects in Agriculture. Int. Res. J. Pure Appl. Chem. 2020, 21, 20–35.
Rahman, M., Mukta, J., Sabir, A., et al. (2018). M. Chitosan biopolymer promotes yield and stimulates accumulation of antioxidants in strawberry fruit. PLoS ONE, 13, e0203769.
Rodrigues, M., Baptistella, J. L., Horz, D. C., et al. (2020). Organic Plant Biostimulants and Fruit Quality—A Review. Agronomy, 10(7), 988. https://doi.org/10.3390/agronomy10070988
Rouphael, Y., Giordano, M., Cardarelli, M., et al. (2018). Plant- and seaweed-based extracts increase yield but differentially modulate nutritional quality of greenhouse spinach through biostimulant action. Agronomy, 8, 126
Tahiri, A., Meddich, A., Raklami, A., et al. (2021). Assessing the potential role of compost, PGPR, and AMF in improving tomato plant growth, yield, fruit quality, and water stress tolerance. Journal of Soil Science and Plant Nutrition, 22(1), 743–764. https://doi.org/10.1007/s42729-021-00684-w
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