Chitosan, a natural polysaccharide biopolymer, is widely recognized for its excellent biocompatibility, antibacterial properties, and growth – promoting effects. These unique characteristics make it an ideal candidate for seed treatment, offering sustainable and effective solutions for modern agriculture.
Primary Methods of Chitosan - Based Seed Treatment
1. Solution Soaking Method
The solution soaking method is the most commonly used approach for chitosan – based seed treatment, enabling seeds to absorb active components effectively.
Procedure:
Solution Preparation: Chitosan solutions typically range from 0.1% – 2% (w/v). To dissolve chitosan, dilute acids such as acetic acid or citric acid are required, and the pH should be adjusted to 5.0 – 6.5.
Seed Pretreatment: Select plump seeds, wash them thoroughly with clean water, and then air – dry.
Soaking Process: Immerse the seeds in the chitosan solution at a temperature of 20 – 30°C. The soaking time varies according to the crop type, usually lasting 6 – 24 hours.
For example:
Rice Seeds: Soaking rice seeds in a 1% chitosan solution for 12 hours can significantly enhance the germination rate and improve the cold resistance of seedlings.
Tomato Seeds: A 0.5% chitosan solution, when used for an 8 – hour soak, promotes root development and enhances the growth of tomato seedlings.
Post – treatment: After soaking, rinse the seeds with clean water and either air – dry them or sow them directly.
2. Seed Dressing Method
In the seed dressing method, chitosan solution is mixed with seeds to form a thin – layer coating.
Steps:
Solution Preparation: Prepare a low – concentration chitosan solution (0.05% – 0.5%). Spray or mix the solution with seeds at a ratio of 5% – 10% of the seed weight.
Drying: After thorough mixing, air – dry the seeds to ensure that chitosan adheres evenly to the seed surface.
Advantages: This method is simple and practical, making it suitable for large – scale treatment of cereal seeds such as wheat and corn.
3. Seed Coating Method
The seed coating method involves formulating chitosan with other functional components, such as fertilizers, fungicides, and trace elements, to create a protective coating layer.
Typical Formulation:
Chitosan (1% – 3%) + Sodium Alginate (0.5% – 1%) + Trace Elements (e.g., Zn, Mn) + Bioactive Substances (e.g., auxins).
Process:
Preparation of the mixed solution → Spray – coating on seeds → Drying and curing → Sowing.
Application Example: When cucumber seeds are coated with a chitosan – based mixture, the germination rate increases by 15% – 20%, and the seedlings show significantly enhanced resistance to fusarium wilt.
Mechanisms of Chitosan - Mediated Seed Treatment
1. Promotion of Seed Germination and Seedling Growth
Chitosan can enhance the activity of seed enzymes, such as α – amylase and protease, accelerating the decomposition of starch and proteins, thereby providing energy for germination.
Additionally, it improves seed water – absorption capacity, facilitating radicle emergence and shortening the germination time.
2. Induction of Plant Disease Resistance
As an elicitor, chitosan can induce the production of phytoalexins (e.g., flavonoids) and pathogenesis – related proteins (PR proteins) in seeds, strengthening their resistance against fungi (such as Fusarium) and bacteria. Moreover, chitosan can inhibit pathogen growth by disrupting the fungal cell wall and suppressing spore germination. For instance, it can inhibit the growth of Alternaria solani, the causal agent of early blight in tomatoes, with an inhibition rate of over 70%.
3. Improvement of Root Development and Nutrient Uptake
Chitosan promotes root cell division and elongation, increasing the number of fibrous roots and expanding the absorption area. Its degradation products, oligosaccharides, can act as signaling molecules to regulate the uptake and transport of nutrients like nitrogen and phosphorus in roots.
Treatment Effects and Optimization Strategies for Different Crops
| Crop Type | Treatment Concentration | Treatment Time | Main Effects | |
|---|---|---|---|---|
| Rice | 0.5% – 1.5% | 12 – 24 h | Germination rate increased by 10% – 15%; enhanced cold resistance | |
| Wheat | 0.2% – 0.8% | 8 – 16 h | Root fresh weight increased by 20%; improved drought resistance | |
| Vegetables (Tomato, Cucumber) | 0.3% – 1.0% | 6 – 12 h | Seedling height and stem diameter increased by 15% – 30%; enhanced disease resistance | |
| Oilseed Crops (Soybean) | 0.1% – 0.5% | 8 – 10 h | Increased nodulation number; improved nitrogen – fixing ability |
Application Prospects
As a green and environmentally friendly seed treatment agent, chitosan has the potential to replace some chemical pesticides and hormones, thanks to its dual functions of promoting growth and enhancing disease resistance. Future research directions include:
Developing nano – scale chitosan formulations to improve seed absorption efficiency.
Employing gene sequencing technology to elucidate the disease – resistance signaling pathways induced by chitosan.
Optimizing chitosan formulations for special environments such as saline – alkali soils and arid regions to enhance crop stress tolerance.