Seed biopriming for sustainable agriculture and ecosystem restoration

Abstract

The utilization of microbial inoculants in the realm of sustainable agricultural and ecosystem restoration has witnessed a surge in recent decades. This rise is largely attributed to advancements in our understanding of plant-microbe interactions, the urgency to reduce the dependence on agrochemicals and the growing societal demand for sustainable strategies in ecosystem management. However, despite the rapid growth of bio-inoculants sector, certain limitations persist concerning their efficacy and performance under the field condition. Here, we propose that seed biopriming, an effective microbial inoculant technique integrating both biological agents (the priming of beneficial microbes on seeds) and physiological aspects (hydration of seeds for improved metabolically activity), has a significant potential to mitigate these limitations. This method increases the protection of seeds against soil-borne pathogens and soil pollutants, such as salts and heavy metals, while promoting germination rate and uniformity, leading to overall improved primary productivity and soil health. Furthermore, we argue that a microbial coating on seeds can facilitate transgenerational associations of beneficial microbes, refine plant and soil microbiomes, and maintain soil legacies of beneficial microflora. This review article aims to improve our understanding of the seed biopriming approach as a potent and valuable tool in achieving sustainable agriculture and successful ecosystem restoration.

FIGURE 1

Transmission of seed microbiomes across generations: implications for ecosystem function and legacy effects. Seed microbiomes serve as the origin of plant microbiomes, encompassing both endophytic and surface‐attached microorganisms. These microbes maintain intimate associations with plants and their ecological functions, which are becoming increasingly evident in terms of plant and ecosystem health. They contribute to seed health, seed germination and overall plant vitality. For instance, seeds contaminated by fungal infections due to fungal spores and high humidity of the environment can result in infection‐induced reduction in germination rates. Seed microbiomes not only contribute to the plant microbiome in the roots and phyllosphere but also that in the flowers and fruits, along with significant contribution from soil microbiomes, as demonstrated in processes (1) through (5) in the figure. Crucially, certain plant and soil microbial components are retained and transmitted to seeds, which are then carried over to subsequent plant life cycles. A healthy seed microbiome is also vital for maintaining the functionality of both above‐ and below‐ground ecosystems. This includes promoting plant biomass production, improving food quality and safety, preserving high soil organic matter content, and regulating the abundance of soil pathogens. Evidence also suggests that insects, such as pollinators, may facilitate microbial transmission between plants and also potentially across different plant generations (Hannula et al., 2019). However, the impact of insects in this process can be both beneficial and detrimental, depending on various unexplored biotic and abiotic factors, as illustrated by process (6).

FIGURE 2

Seed biopriming process and its positive effects on seed vigour and plant health. Seed biopriming is a pre‐sowing seed treatment process in which seeds are inoculated with beneficial microorganisms, such as mycorrhizal fungi, nitrogen‐fixing bacteria, plant growth‐promoting rhizobacteria (PGPR), and biological control agents (BACs). It includes seed hydration and incubation steps, which can establish microbial protective layer around the seeds and facilitates superior microbial encapsulation while simultaneously triggering seed metabolic activities. Seed biopriming can strongly enhance plant health by facilitating nutrient uptake and increasing resistance to both biotic and abiotic stresses. The benefits of priming are primarily associated with the induction of biochemical, molecular and cellular events that promote cell repair mechanisms. These mechanisms can help restore cellular integrity and are mediated by synthesis of nucleic acids (RNA and DNA) and proteins, as well as the enhancement of antioxidant defence mechanisms. Seed dormancy is an obstacle to seed germination and is usually influenced by both internal and external factors, such as hormones, metabolic activities, temperature, light, water and oxygen. Seed priming activates enzymes responsible for mobilizing reserve substances, such as α‐ and β‐amylases for carbohydrate breakdown and isocitrate lyase for lipid breakdown. By influencing hormones (e.g. abscisic acid and gibberellins) and metabolic activities (e.g. synthesis and degradation of storage compounds and enzymes) in seeds, biopriming can contribute to improved seed vigour, seed germination, and seedling emergence. Moreover, it has been suggested that the success of seed biopriming can be influenced by numerous factors, such as the microorganisms used, plant selection (e.g. plant species and genotype), interactions with native microbial communities, and environmental conditions (e.g. climatic and edaphic factors).

FIGURE 3

A conceptual framework for seed microbiome engineering and developing effective microbial tools for enhancing plant health and productivity. Identifying innovative strategies to engineer seed microbiomes for healthier plants is vital for agriculture and environmental sectors. Generally, seed treatments create seed products that land managers use to boost seed germination, and land productivity, and the process primarily involves seed coatings with microbes and/or chemical agents, also referred to as pro/prebiotic coatings. The prebiotics can directly enhance seedling growth and/or indirectly attract beneficial microbes present in the soil, rhizosphere and roots. Integration of multi‐omics tools with traditional chemical and microbial isolation and identification is providing researchers with more profound insights into seed microbiomes and the chemical mediators that facilitate beneficial plant–microbe interactions, such as organic compound‐based chemical signals. Utilizing these key microbes and identified organic signals for seed treatments may result in healthier and more productive plant seeds. Furthermore, the emerging technique of coating seeds with nanoparticles also offers a promising approach to developing commercial seed products with higher germination rates and improved plant vigour.