Microbial seed treatments are a game-changer in germination, leveraging the power of beneficial microorganisms to enhance seed germination rates, protect seedlings, and promote robust early growth. By inoculating seeds with microbes like plant growth-promoting bacteria (PGPB), rhizobia, and mycorrhizal fungi, farmers can kickstart plant development from the very beginning. Natural products like worm castings and biological brews, such as Worm Brew, amplify these benefits by delivering diverse microbial communities directly to seeds and seedling mixes. This blog post delves into the microbiology behind these treatments, their role in accelerating germination and protecting seeds, and how worm castings and biological brews supercharge these processes, supported by scientific studies.
The Microbiology of Seed Success
Microbial seed treatments involve applying beneficial microorganisms - primarily bacteria and fungi - to seeds before planting. These microbes form symbiotic relationships with plants, colonising the seed surface and the surrounding spermosphere (the soil zone around a germinating seed). Key players include Bacillus subtilis, Pseudomonas fluorescens, Rhizobium spp., Trichoderma harzianum, and arbuscular mycorrhizal fungi (AMF). These organisms work together to enhance germination, protect against pathogens, and improve nutrient uptake, giving seeds a head start in life.
Accelerating Germination Through Microbial Activity
Beneficial microbes trigger biochemical processes that speed up seed germination. PGPB like Bacillus subtilis and Pseudomonas spp. produce enzymes and phytohormones, such as gibberellins and auxins, which break seed dormancy and stimulate metabolic activity during the imbibition phase (when seeds absorb water). A study by Lastochkina et al. (2020) demonstrated that wheat seeds treated with Bacillus subtilis strain 10-4 exhibited faster germination and higher seedling vigour, with germination rates reaching up to 100% under suboptimal conditions [1]. These microbes also synthesise antioxidants, reducing oxidative stress during germination and ensuring uniform seedling emergence.
Mycorrhizal fungi, such as Glomus spp., further enhance germination by forming symbiotic networks with seedling roots. These fungi extend the root surface area, improving water and nutrient absorption, which is critical for rapid establishment. Research on Quercus ilex (holm oak) showed that seeds with native microbial communities, including endophytic fungi, germinated significantly faster than sterilised seeds, underscoring the role of early microbial colonisation in breaking dormancy and accelerating growth [2].
Protective Microbial Shields
Microbes form a living shield around seeds, protecting them from soil-borne pathogens and environmental stresses. Antagonistic bacteria like Bacillus and Pseudomonas spp. produce antimicrobial compounds, such as lipopeptides and siderophores, that suppress pathogens like Pythium and Rhizoctonia, which cause damping-off diseases. A study on maize seeds inoculated with Trichoderma harzianum found a significant reduction in fungal infections, with seedling emergence rates improved by up to 30% [3]. These microbes also induce systemic resistance in plants, priming their immune systems to fend off future attacks.
Additionally, microbes mitigate abiotic stresses like salinity and drought. Nitrogen-fixing bacteria, such as Azospirillum spp., enhance nutrient availability by converting atmospheric nitrogen into plant-usable forms, supporting seedling growth in nutrient-poor soils. A greenhouse study on chickpea seeds treated with Paenibacillus lentimorbus showed improved germination and drought tolerance, as the bacteria formed a biofilm that retained moisture and nutrients around the seed [4].
Early Colonisation for Long-Term Benefits
The presence of beneficial microbes at the start of a plant’s life cycle is critical for establishing a healthy microbiome. Seed-borne endophytes and soil microbes colonise the spermosphere and rhizosphere (the root-soil interface), creating a supportive microbial ecosystem. This early colonisation enhances root development, nutrient uptake, and stress resilience. By applying microbes directly to seeds, farmers ensure these beneficial organisms are present from day one, maximising their impact on germination and early growth.
Worm Castings and Biological Brews: Microbial Powerhouses
Worm castings and biological brews like Worm Brew are natural, microbe-rich products that deliver these benefits directly to seeds and seedlings. Their diverse microbial communities and organic matter make them ideal for seed dressing and incorporation into seedling mixes. There are many ways to achieve this - produce the worm cast and brew yourself (check out our Worm Mod's) or purchase a ready to go worm cast liquid concentrate from us (check out Worm Brew).
Worm Castings: A Microbial Haven for Seedlings
Worm castings, the nutrient-rich excrement of earthworms, are teeming with beneficial microbes, including Bacillus, Pseudomonas, and actinomycetes, as well as mycorrhizal fungi. These microbes colonise the seed surface and spermosphere, creating a protective and nutrient-rich environment. Research from Cornell University highlights that the microbial communities in worm castings produce antimicrobial compounds that disrupt pathogen signaling, reducing infection rates in seedlings [6]. When mixed into seedling substrates, worm castings improve soil structure, water retention, and nutrient cycling, fostering optimal conditions for germination.
A study from South Carolina State University found that seeds planted in mixes with worm castings exhibited higher germination rates and stronger seedlings compared to those in standard potting soil [7]. The microbes in castings enhance nutrient availability by breaking down organic matter into plant-accessible forms, particularly nitrogen and phosphorus. This is especially beneficial for seedlings grown from cuttings, as the microbial activity in castings mitigates transplant shock and supports robust root development.
Biological Brews: Liquid Microbial Boosters
Biological brews, such as our Worm Brew, are liquid extracts derived from vermicast or compost, packed with living microbes like bacteria, fungi, and actinomycetes. When used as a seed dressing, these brews coat seeds with a diverse microbial inoculum, ensuring immediate colonisation upon planting. A little also goes a long way, for example, 20L of Worm Brew coats 1 tonne of seeds! These interactions improve nutrient uptake, suppress pathogens, and buffer environmental stresses like pH imbalances.
Applying biological brews is simple: seeds are lightly coated with the liquid as they're going out. Trials with vermicast-based inoculants demonstrated that treated seeds developed denser root systems and stronger seedlings, particularly in degraded or nutrient-poor soils [8]. The fungal dominance in these brews supports mycorrhizal associations, which enhance water and nutrient absorption, leading to faster germination and healthier plants.
Make your own!
If you have the time and want to explore producing your own biological brews, get in touch with the team and we can walk you through basic recipes to get you started. Alternately, if you're wanting to test out microbial seed dressings, our Worm Brew can be purchased in 20L, 200L, and 1000L containers to get you started. We often say that a seed dressing is a great way to get the best bang for your buck. Of course, additional applications only magnify the above benefits even further.
Want to talk about your operation specifically? Chat to the team on 07 3195 6969 or email us at admin@wormsdownunder.com
References
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Lastochkina, O., et al. (2020). Seed priming with Bacillus subtilis enhances wheat germination and seedling growth under stress. Plants, 9(11), 1512.
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Llabrés, M. T., et al. (2021). Seed-associated microbial communities enhance germination in Quercus ilex. Plant and Soil, 467, 351–364.
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Harman, G. E. (2006). Trichoderma species for biocontrol of soil-borne plant pathogens. Nature Reviews Microbiology, 4, 43–56.
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Khan, N., et al. (2018). Paenibacillus lentimorbus enhances chickpea germination under drought stress. Frontiers in Microbiology, 9, 1883.
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Choudhury, A. R., et al. (2019). Azotobacter inoculation improves rice seedling growth. Journal of Plant Nutrition, 42(15), 1803–1814.
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Edwards, C. A., et al. (2006). The role of earthworm castings in soil fertility and plant growth. Soil Biology and Biochemistry, 38, 145–156.
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Arancon, N. Q., et al. (2004). Effects of vermicomposts on plant growth. Bioresource Technology, 93, 145–153.
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Jack, A. L. H., et al. (2011). Vermicompost extracts enhance microbial activity and plant growth. Applied Soil Ecology, 49, 217–223.
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O’Callaghan, M. (2016). Microbial inoculation of seeds for improved crop performance. Applied Microbiology and Biotechnology, 100, 5729–5746.