What Are Post-Harvest Diseases?
- Post-harvest diseases refer to the illnesses that develop in harvested plant materials, including seeds, fruits, and vegetables. These diseases may manifest after the initial harvest and can occur at various points during the distribution chain—such as during transport to storage facilities, while in storage, or just prior to consumption. Importantly, some infections may originate in the field but remain asymptomatic until the harvested products are handled or stored.
- The onset of post-harvest diseases is typically attributed to microorganisms, which can lead to significant deterioration, including rotting and decay. These infections can compromise both the quantity and quality of agricultural products. For instance, the presence of certain pathogens can result in the accumulation of harmful substances known as mycotoxins, which pose health risks to consumers.
- Fleshy fruits and vegetables, such as tomatoes, bananas, citrus fruits, strawberries, ginger rhizomes, onions, and potatoes, are particularly susceptible to post-harvest diseases. These infections not only decrease the marketable quantity but can also adversely affect the overall quality of the products. Consequently, understanding the dynamics of post-harvest diseases is crucial for farmers, distributors, and consumers alike.
- The degree of damage caused by post-harvest diseases is influenced by several factors, including the specific pathogens involved, the condition of the harvested products, and the environmental conditions during storage. Common pathogens responsible for post-harvest diseases include various fungi, such as Pythium, Phytophthora, Rhizopus, and Aspergillus, as well as certain bacteria, notably Pseudomonas and Erwinia.
- To effectively mitigate the impact of post-harvest diseases, it is essential to implement rigorous management strategies. These may include optimal harvesting practices, careful handling to minimize damage, appropriate storage conditions to inhibit pathogen growth, and the use of fungicides or biological control methods to prevent infections. By prioritizing these approaches, stakeholders in the agricultural supply chain can enhance the preservation of harvested products and ultimately contribute to food security.
Classification of Post-Harvest Diseases
Post-harvest diseases can be classified based on the timing of pathogen infection, specifically focusing on two primary categories: field pathogens and storage pathogens. This classification aids in understanding the nature and timing of infections that affect harvested plant products, allowing for more effective management strategies.
- Field Pathogen:
- Definition: Field pathogens are microorganisms that cause infections in plants or their products while they are still developing in the field, prior to harvest.
- Infection Timing: These pathogens initiate infections during the growth stages of the plant, leading to potential disease development that may not be readily observable at the time of harvesting.
- Symptoms: In many cases, symptoms associated with field pathogens can remain inconspicuous until after the product is harvested. In fleshy and juicy fruits and vegetables, infection can continue to progress post-harvest.
- Continued Infection: Even after harvest, products may become infected by the same field pathogens or other pathogens present in the storage environment. This ongoing susceptibility necessitates careful handling and storage to minimize disease spread.
- Storage Pathogen:
- Definition: Storage pathogens are microorganisms that infect plant products during storage, often exploiting any vulnerabilities that may have developed prior to or during harvest.
- Infection Dynamics: Unlike field pathogens, storage pathogens may initiate infections exclusively during the storage phase. However, they can also infect produce that was already compromised by field pathogens before harvest.
- Impact on Seeds and Grains: In the case of seeds and grains, diseases caused by field pathogens tend to cease developing shortly after harvest. Nevertheless, these products can still be vulnerable to infections by storage pathogens during the storage phase, leading to significant losses.
Types of Post-Harvest Diseases
Post-harvest diseases are critical factors affecting the quality and safety of stored agricultural products. Based on the classification by Stackmann and Harrar (1957), these diseases can be grouped into two primary categories: diseases affecting dry, bulk materials such as seeds and grains, and diseases impacting fleshy storage organs like vegetables and fruits. Understanding these categories helps in developing effective management strategies to mitigate spoilage.
- Diseases of Dry, Bulk Materials:
- Overview: This category primarily includes seeds and grains that are stored in bulk. The risk of spoilage arises from specific environmental conditions and pathogen interactions.
- Pathogen Dynamics: Field fungi, including Alternaria, Fusarium, Cladosporium, Verticillium, and Helminthosporium, can initially infect seeds and grains during the growing phase. However, they typically do not thrive in storage conditions due to the low relative humidity, which is generally below 90%.
- Storage Fungi: During transit and storage, seeds and grains may become susceptible to various species of Aspergillus and Penicillium, which can proliferate in relative humidity levels ranging from 70% to 90%. Common species of Aspergillus include A. repens, A. ruber, A. flavus, and A. candidus.
- Impact on Seed Viability: These storage fungi can invade the seed embryos, causing discoloration and significantly reducing germination rates. Moreover, high temperatures can develop during storage, sometimes exceeding 70°C, encouraging the growth of thermophilic fungi such as Aspergillus fumigatus, Absidia spp., and Mucor pusillus.
- Mycotoxin Production: Various fungi produce mycotoxins during storage, posing severe health risks to humans and domestic animals. Key fungi involved in mycotoxin production include Aspergillus and Penicillium, which can produce aflatoxins and other harmful toxins.
- Types of Mycotoxins:
- Yellow Rice Toxins: These toxins are produced by species of Penicillium and can contaminate grains such as rice and barley.
- Tremorgenic Toxins: These are formed on prepared food stored under refrigeration or other conditions, as well as on foods made from infected grains and seeds.
- Penicillic Acid: This carcinogenic compound is generated by various species of Aspergillus and Penicillium in moldy cereal grains, highlighting the significant health hazards posed by these pathogens.
- Diseases of Fleshy Storage Organs:
- Overview: This group focuses on the spoilage of fleshy fruits and vegetables, such as tubers, rhizomes, and bulbs. The risk of disease is often exacerbated by high moisture content, temperature, and physical injuries during handling.
- Pathogen Factors: Fleshy fruits and vegetables are particularly susceptible to attack by pathogenic organisms due to their high moisture content and nutrient-rich environment, which can support pathogen growth.
- Impact of Injuries: Physical injuries inflicted during harvesting, packing, and transportation provide entry points for pathogens, leading to accelerated spoilage. Unlike seeds and grains, which can be stored for extended periods under controlled moisture conditions, fleshy storage organs require more stringent management to minimize pathogen proliferation.
Control of Post-Harvest Diseases
Controlling post-harvest diseases is essential for maintaining the quality and safety of agricultural products. Effective management strategies involve a combination of preventative measures and treatments aimed at minimizing infection and spoilage. Below is a comprehensive overview of various control methods that can be employed to manage post-harvest diseases effectively.
- Careful Harvesting and Handling:
- Fruits and vegetables must be harvested with care to prevent injuries, which can serve as entry points for pathogens. Proper handling techniques help maintain the integrity of the produce throughout the harvesting process.
- Removal of Infected Areas:
- Any infected regions on vegetables should be promptly removed to prevent the spread of pathogens during transportation and storage. This practice limits the potential for further infection and preserves the overall quality of the remaining product.
- Sanitation of Storage Facilities:
- Thorough cleaning of storage containers and warehouses is critical to prevent contamination. Utilizing disinfectants such as copper sulfate (CuSO₄) or formaldehyde can significantly reduce pathogen load in these environments.
- Temperature Control:
- Maintaining a low storage temperature is crucial for inhibiting the development of post-harvest diseases. Cooler temperatures slow down the metabolic processes of pathogens, thereby reducing their growth and impact on the stored products.
- Ventilation:
- Ensuring proper ventilation within storage areas helps mitigate the spread of pathogens. Adequate airflow reduces humidity levels, making the environment less conducive for pathogen development.
- Pest Management:
- Keeping crops free from insects and other pests is vital. By preventing pest infestations, producers can minimize the risk of creating new wounds on the produce, which could become points of entry for pathogens.
- Thermal Treatments:
- Employing hot water or hot air treatments can effectively reduce the incidence of disease. These methods can kill or inactivate many pathogens, thereby providing a physical means of controlling post-harvest diseases.
- Chemical Control Measures:
- The application of fungicides, such as thiabendazole, dichloran, and dosa-ash, can help control post-harvest diseases by preventing infections and suppressing pathogen development on the surface of the host products. These chemicals serve as a protective barrier against a wide range of pathogens.
- Supplementary Chemical Treatments:
- Additional chemical treatments, such as the use of acetaldehyde vapors and biphenyl/nitrogen chloride compounds, can be employed as supplementary measures. These chemicals help enhance the control of post-harvest diseases during storage and transportation.
