BOTRYTIS CINEREA: CHARACTERISTICS, TAXONOMY, SYMPTOMS, CONTROL - BIOLOGY - 2025

Botrytis cinerea is a pathogenic filamentous fungus that affects a wide variety of economically important horticultural and fruit crops. Known as gray mold or gray rot, it is an ascomycete of the Sclerotiniaceae family that primarily attacks bulbs, leaves, flowers and fruits.

It is a necrotrophic fungus capable of developing on wounds and damaged, senescent or dead tissues of various hosts. It reproduces mainly through asexual conidia or spores, whose masses of gray conidia are easily dispersed through wind, water or any physical activity.

Botrytis cinerea affecting grape cultivation. Source: Photographer: Tom MaackNo machine-readable author provided. Tom ~ commonswiki assumed (based on copyright claims). / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)

The ideal environments for its propagation are closed spaces with high relative humidity and cool temperatures, such as greenhouses or nurseries. In addition, it is a common pathogen of ornamental plants or crops such as strawberries and grapes, especially during the flowering and fruiting stages.

Symptoms manifest as tissues that darken and soften due to the death of host cells, subsequently covered with a characteristic gray mold. Similarly, the infection can develop on living cells, being visible after 15-20 days. Once installed it is difficult to eradicate by different control methods.

General characteristics

From a morphological point of view, Botrytis cinerea is characterized by the large number of asexual conidia or spores. The oval-shaped conidia are terminally arranged at the end of a long, grayish branched conidiophore.

In low temperature conditions or during winter, the hardened sclerotia or mycelium of the fungus remains in hibernation in the soil. It usually grows on decaying plant debris. When the humidity and temperature conditions are favorable, it disperses the conidia with the help of the wind.

The spores do not penetrate through healthy tissues, they generally initiate the infestation through wounds caused by physical damage, insects or pruning. For this reason, it is important to carry out an effective agronomic management, since, once the crop is infected, its propagation is easily carried out.

The pathogen not only affects crops in full production, but can attack flowers or fruits once harvested, thus it is stored at low temperatures.

As a saprophyte it can survive in a great diversity of cultivated plants and on decomposing material. The conidia are kept for more than a year under storage conditions, although their viability is reduced. In the soil it is not able to survive, unless it remains as sclerotium on organic remains.

Botrytis cinerea conidiophores. Source: Ninjatacoshell / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Taxonomy

- Fungi kingdom

- Edge: Ascomycota

- Class: Leotiomycetes

- Order: Helotiales

- Family: Sclerotiniaceae

- Genus: Botrytis

- Species: Botrytis cinerea Pers., 1801

Etymology

- Botrytis: the name of the genus comes from the Greek «botrys» which means «bunch of grapes».

- cinerea: the specific adjective derives from the Latin «cinerea», alluding to the ashen color of the spores accumulated on the mold.

Symptoms

One of the main symptoms is soft tissue rot in flowers and fruits. The rot begins as a light brown spot with irregular margins.

Later the tissue turns dark in color, but the margins remain a lighter shade. The color of the stain may vary according to the tone of the affected organ.

Small grayish eruptions or efflorescences on affected tissues are common. These colorations are made up of the conidia of the fungus that develop freely.

In the case of flowers, the fungus infection is not appreciated at first. Only when the fungus has settled do pale spots with a dark brown ring form. Later, necrosis of the tissues begins near the site of infection.

It usually appears under conditions of high humidity and cool temperatures. Its incidence is greater in periods of abundant rainfall or any situation in which the plant surface remains humid, such as frequent sprinkling irrigation.

The presence of physical damage or wounds on stems, leaves, flowers and fruits favors the germination of the spores. Its presence is only detected when the affected tissues begin to rot and necrotic spots appear. Eventually the affected tissue becomes covered by a greyish mold.

Botrytis cinerea on strawberry. Source: Rasbak / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)

Commonly affected plants

As mentioned, the Botrytis cinerea fungus affects various commercial crops such as ornamental plants, vegetables and fruit trees. Above all, it affects plantations established in closed spaces such as nurseries or greenhouses, where a cool environment with high relative humidity is maintained.

This phytopathogen can cause serious economic losses in vegetable crops such as artichokes, aubergines, squash, beans, lettuce, cucumbers, peppers, tomatoes and carrots. In fruit trees such as blueberry, strawberry, apple, orange, pear, banana and grape. Also, in wallflower, begonia, cyclamen, carnation, chrysanthemum, dahlia, gerbera, gladiola, iris, lily, rose, tulip and violets.

Control methods

The gray mold or gray rot caused by Botrytis cinerea is one of the most frequent diseases in various crops, and its presence is not a mere coincidence. It is a phytopathogenic fungus that develops under conditions of high relative humidity and cool temperatures.

No commercial or wild crop is exempt from suffering from this disease, since, once the tissues are affected, it is difficult to reverse its development. In addition to this, its propagation is carried out in a simple, fast and effective way.

For this reason, it is advisable to apply cultural control measures, biological control or chemical control, in order to prevent its incidence.

Gray monkey on tomato. Source: Rasbak / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)

Cultural control

The so-called "cultural practices" are a series of actions that make it possible to prevent the appearance of gray mold on commercial crops or garden plants. An effective cultural management focused on avoiding the presence of any phytopathogen such as Botrytis cinerea, requires the following actions:

- Avoid very tight planting densities, especially under conditions of high humidity and low solar radiation. Very dense populations favor the dispersal of the pathogen once it is established in the crop.

- Maintain effective control of aeration, temperature, humidity and irrigation in greenhouses. The excess of humidity favors the development and dispersion of the fungus.

- Once detected, it is necessary to immediately eliminate the infected plants, avoiding contaminating the environment. Gray mold is an extremely infectious fungus and can affect neighboring plants quickly.

- Avoid sudden changes in temperature that can cause moisture condensation inside the greenhouse. The accumulation of drops on the leaves tends to favor the appearance of the fungus.

- When propagating cuttings, cuttings or grafts, it is convenient to treat the wounds with some type of protective or healing gel. Indeed, wounds are the main route of penetration of the fungus and it attacks weak tissues.

- Propagation by seeds requires the use of certified or undamaged seeds.

- Nursery-propagated seedlings should be kept at a certain distance. Gray mold is a highly infected disease that just infecting one plant can spread rapidly throughout the rest of the crop.

- All equipment and tools used inside the greenhouse or nursery must be disinfected in order to prevent the spread of the disease.

- In the same way, users must take care to use adequate and disinfected clothing when moving around their workplace.

Gray jumpsuit on citrus. Source: Veronidae / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Biologic control

Biological control is a technique that allows the use of living organisms to reduce the incidence or impact of a phytopathogenic fungus. Currently, there is a great variety of fungi or bacteria that control gray mold under certain conditions and agronomic management.

This control technique, in addition to being effective, is a practice that respects the environment, since it does not pollute the ecosystem. Similarly, it does not have adverse effects on animals or humans.

Among the main biological control agents against Botrytis cinerea, the following can be mentioned:

- Mushrooms of the genus

Group of filamentous fungi that develop on various substrates, their action includes competition for nutrients or space, and production of secondary metabolites. As well as microparasitism and the stimulation of the defense mechanism of the host plant.

Among the main species, Mucor corymbilfer stands out, which develops on decomposed food, such as moldy bread and Mucor mucedo, which grows on the ground and causes rotting of fruits. Likewise, the Mucor pusillus that grows on moist bread and the Mucor racemosus that grows on decomposing plant material.

- Trichoderma harzianum

It is considered one of the main beneficial fungi for man, being widely used as a biological control agent. It is used in foliar applications and seed treatment to control diseases caused by phytopathogenic fungi.

Its action consists of increasing the capacity of plants to absorb the necessary nutrients to face the attack of gray mold. It is considered an environmentally friendly organism that does not present adverse effects against wild flora or fauna, or human beings.

- Bacillus subtilis

It is considered a cosmopolitan bacterium that grows on various habitats and is widely used as a biological control agent. It is used as a wettable powder that is applied in sprays at a rate of 3-4 kg / Ha in aubergine, strawberry, paprika or tomato crops.

Illustration of Botrytis cinerea. Source: Unknown author / Public domain

Chemical control

Chemical control is based on the application of fungicides. In addition, being expensive, it is often ineffective, since Botrytis cinerea once installed is difficult to eradicate.

An effective chemical control consists of the preventive application of fungicides based on Iprodione 50% P / V, Vinclozolin 50% P / P or Procymidone 50% P / P. Likewise, it is advisable to apply broad-spectrum fungicides during flowering and apply fungal pastes on tissues that present cankers.

Chemical treatment must be accompanied by good agricultural management practices in order to increase the chances of success. An excessive application or use of the wrong fungicide can have negative consequences, even more serious than the attack of the phytopathogen.

References

1. Benito, EP, Arranz, M., & Eslava, A. (2000). Botrytis cinerea pathogenicity factors. Revista Iberoamericana de Micología, 17, S43-S46.
2. Botrytis cinerea. (2020). Wikipedia, The Free Encyclopedia. Recovered at: es.wikipedia.org
3. Botrytis cinerea Pers., 1801 (2017) Catalog of Life: 2020. Retrieved from: catalogueoflife.org
4. Botrytis cinerea or gray rot (2020) Agromatic. Recovered in: agromatica.es
5. Calvo Garrido, C. (2014). Control of Botrytis cinerea rot by applying Candida sake CPA-1 and other alternative strategies to chemical fungicides in wine grapes (Doctoral dissertation, Universitat de Lleida).
6. Cano, MA (2013). Biological strategies for disease management in strawberry cultivation (Fragaria spp.). Colombian Journal of Horticultural Sciences, 7 (2), 263-276.
7. García, I. (2018) Botrytis cinerea: a highly infectious crop killer - detailed. Recovered in: canna.es
8. Koike, S., & Bolda, M. (2016). Gray Mold, or Strawberry Rot. UC Cooperative Extension. Santa Cruz. Recovered at: ucanr.edu
9. Gray Rot (2018) Seminis Vegetable Seeds, Inc. Recovered at: seminis-las.com
10. Techniques for the control of Botrytis (2016) ABC Agro: Chilean Agricultural Portal of Infoagro.com. Recovered at: abcagro.com