What food does Alternaria grow on?

November 28, 2025 •

4 min read

Alternaria is a widespread fungal genus known to cause significant pre- and post-harvest damage to a variety of agricultural products. This mold thrives on numerous foods, compromising their quality, safety, and commercial value.

Quick Summary

This article details the wide range of foods, including fruits, vegetables, and grains, susceptible to contamination by the Alternaria fungus. It explores the conditions for its growth, the resulting black rot and spoilage, and the potential health concerns from associated mycotoxins.

Key Points

Diverse Hosts: Alternaria grows on a wide variety of foods, including fruits like tomatoes, apples, and citrus, vegetables such as carrots and broccoli, and cereals like wheat and sorghum.
Causes 'Black Rot': The fungus is notorious for causing 'black rot' and 'black spot' diseases, leading to visible dark lesions and internal decay in produce.
Pre- and Post-harvest Threat: Contamination can occur in the field before harvest or during refrigerated storage and transport, with infection often starting through wounds or natural openings.
Produces Mycotoxins: Many Alternaria species produce mycotoxins (e.g., AOH, AME, TeA) that can be harmful to human and animal health when ingested.
Requires Specific Conditions: Optimal growth occurs in warm, humid conditions, but the mold can produce toxins even at low temperatures and low water activity, making it a persistent problem.
Control Measures are Key: Prevention strategies include using clean seed, crop rotation, sanitation, and proper handling and storage techniques to minimize spoilage and toxin production.
Impact on Food Quality and Safety: Beyond visual damage, Alternaria contamination compromises food quality and presents a food safety concern due to the risk of mycotoxin exposure.

Common Alternaria hosts: Fruits, vegetables, and cereals

Alternaria is a ubiquitous fungus that can be found in soil, water, and air, making it a common contaminant for many crops, both in the field and during post-harvest storage. The mold is particularly problematic due to its ability to grow and produce toxins even under refrigerated conditions, leading to considerable spoilage of perishable goods.

Fruits

Many fruits are highly susceptible to Alternaria contamination, particularly after harvest, during transport, and in storage.

Apples: Alternaria is a well-known cause of core rot and moldy core in apples.
Citrus Fruits: Species such as Alternaria citri are responsible for black rot in oranges, lemons, mandarins, and grapefruits.
Tomatoes: A common contaminant in tomatoes and tomato-based products, causing black rot.
Berries: Can affect grapes and other berries.
Pomegranates: Causes Alternaria fruit rot, also known as black heart.
Figs: Both fresh and dried figs are vulnerable to this mold.

Vegetables

Alternaria is a significant pathogen for a wide array of vegetables, often causing leaf spots, rots, and other diseases.

Carrots: Alternaria radicina causes black rot in both the crown and root.
Brassica Crops: A primary cause of black spot and head rot in vegetables like broccoli, cauliflower, cabbage, and kale.
Peppers: Known to cause Alternaria fruit rot, especially when fruit is damaged by sunscald or insects.
Cucumbers and Melons: These are also known hosts for Alternaria species.

Cereals and Grains

Alternaria species are one of the most common mycotoxigenic fungal genera found in grains worldwide.

Wheat, Sorghum, and Barley: Can cause "black point," a disease that discolors the grain and impairs quality.
Rice and Maize: Less susceptible than smaller grains but can still be infected.

Factors influencing Alternaria growth

The growth and mycotoxin production of Alternaria are significantly influenced by environmental conditions, particularly moisture and temperature. While the mold can tolerate a wide range of temperatures, from near freezing to 35°C, it thrives in warm, humid conditions.

Comparison of Pre-harvest vs. Post-harvest Contamination


Feature	Pre-Harvest Contamination	Post-Harvest Contamination
Mechanism	Infection occurs in the field, often through open flowers, wounds, or natural openings.	Molds grow during transport and storage, thriving in humid environments.
Entry Points	Natural openings (e.g., navel of oranges, petal falls in pomegranates), insect damage, physical wounds.	Wounds from harvesting, processing, or packaging.
Key Conditions	Rainy, high humidity weather, and warm temperatures favor spore production and release.	High moisture content and storage at suboptimal temperatures, even refrigeration.
Visible Signs	Can be difficult to detect initially, as internal decay may not be visible externally.	External black or dark green spots, sunken lesions, and obvious decay.
Control Focus	Field management, sanitation, and resistant cultivars.	Proper handling, temperature control, and sorting to remove damaged produce.

The risks associated with Alternaria mycotoxins

In addition to causing physical food spoilage, many Alternaria species produce mycotoxins, which are harmful secondary metabolites. These toxins can pose a threat to human and animal health when contaminated food is consumed. Some of the most studied Alternaria mycotoxins include alternariol (AOH), alternariol monomethyl ether (AME), tenuazonic acid (TeA), and altertoxins.

Some research has suggested links between Alternaria mycotoxin exposure and health issues like esophageal cancer, particularly in regions with high consumption of contaminated grains. However, toxicological data are still limited, and more studies are needed to fully understand the long-term effects. The European Food Safety Authority (EFSA) and other bodies continue to assess the risks associated with these mycotoxins.

Control and prevention strategies

Controlling Alternaria requires a multi-pronged approach that begins in the field and extends through to storage and processing.

Field Management:

Use certified, disease-free seeds to prevent initial contamination.
Practice crop rotation to reduce fungal buildup in the soil.
Remove infected crop debris after harvest to reduce overwintering pathogens.
Control weeds, as some can serve as hosts for Alternaria.
Choose resistant cultivars where available.

Harvest and Post-Harvest Handling:

Minimize damage to fruit and vegetables during harvest to reduce entry points for infection.
Harvest crops at optimal maturity, avoiding over-ripening.
Implement proper sorting and grading to remove any damaged or already infected produce before storage.
Maintain appropriate storage conditions, including cool temperatures and controlled humidity.

Conclusion

Alternaria is a persistent and common food contaminant, impacting a wide range of agricultural products including fruits, vegetables, and grains. The mold's ability to cause significant pre- and post-harvest spoilage, coupled with the production of potentially harmful mycotoxins, presents both economic losses and food safety risks. While research continues to clarify the full toxicological impact of these mycotoxins, understanding the hosts and implementing effective control strategies—from clean seed to careful storage—are crucial steps for minimizing contamination and protecting food safety. Consumers should inspect produce for black spots or decay and practice proper food storage to mitigate risks.

Frequently Asked Questions

On food, Alternaria contamination typically appears as dark, circular spots that often have concentric rings, sometimes with a yellow halo. The lesions can be sunken, and the affected tissue beneath may be discolored or rotting. A fuzzy, black fungal growth may also be visible in humid conditions.

Some Alternaria species produce mycotoxins that are potentially harmful when ingested. While toxicological data is still limited, some studies suggest links between these toxins and health issues, such as genotoxic, mutagenic, and potentially carcinogenic effects. The European Food Safety Authority (EFSA) continues to monitor and assess their risks.

Yes, Alternaria is capable of growth and mycotoxin production even under refrigerated conditions, which is why it can be a significant contaminant for fruits and vegetables in storage. Cooling can slow its growth but does not always prevent it entirely.

Black point is a disease in small-grain cereals like wheat and barley caused by Alternaria and other fungi. It results in a discoloration of the germ and seed, impacting the grain's quality and affecting products like flour and pasta.

Preventing Alternaria involves careful practices from the field to the kitchen. At home, you can minimize growth by properly storing food at cool temperatures, consuming produce promptly, and discarding any food with visible mold. Buying undamaged produce and reducing water stress during cultivation also helps.

For mold like Alternaria, it is generally unsafe to eat the contaminated food. While some firm, low-moisture foods might be salvageable by cutting out the moldy section, Alternaria mycotoxins can permeate deeper than the visible mold, and it's best to discard the entire item for safety.

Yes, Alternaria is a common source of allergens. Inhaling Alternaria spores can cause respiratory problems, such as allergies and asthma, particularly in late summer and early autumn when spore counts are high.