BOTRYTIS: CHARACTERISTICS, TYPES, SYMPTOMS, CONTROL - BIOLOGY - 2025

Botrytis is a genus of imperfect phytopathogenic fungi belonging to the Sclerotinicaeae family of the Ascomycota division. They develop in environments with a mild and humid climate, being the causative agent of the disease known as gray mold or gray rot.

It is a group of fungi with septate, branched and septate mycelium, which produce endogenous ascospores capable of infecting numerous economically important crops. The spongy, dark-gray mycelium on damaged tissues is a particular characteristic of this group of fungi.

Conidia and conidiophores of the fungus of the genus Botrytis. Source: Heiko4 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

The wounds are the entrance door of its spores, once inside the host it causes the rot of roots, stems, leaves, flowers, fruits, bulbs or tubers. It is considered a necrotrophic fungus, since it presents a parasitic and a saprophytic phase, since after killing the host it continues to feed on its remains.

Its presence is common in greenhouses or grow houses, where vegetables or fruit trees are produced under controlled conditions, including flowers and ornamental plants. Among the main crops that it infects, vegetables (artichoke, pumpkin, lettuce, tomato, paprika), fruit trees (citrus, strawberry, vine), and ornamentals (carnations, geraniums, sunflower, rose, tulips) stand out.

General characteristics

Mycelium

The mycelium is the vegetative part of the fungus, it is made up of pluricellular, cylindrical and septate filaments of apical growth, known as hyphae. The genus Botrytis is characterized by the production of a large number of asexual spores or oval conidia that are located at the end of the conidiophores.

Conidiophores / conidia

The grayish conidiophores originate from the mycelium, although under certain circumstances they are formed from the sclerotia. Conidia are the main dispersal and reproduction structures of the fungus, being a structure that can survive under adverse conditions.

The conidia adhere to the plant surface, maintain their infective capacity and viability during the growth of the culture until they penetrate the host through a wound. Once installed, they generate a small vesicle from which the phialides arise at the end of which the microconidia are produced.

Chlamydospores are formed after transformation of the mycelium and are released as the hyphae break down. They are hyaline in appearance and present a great variability in terms of shape and size, appearing on aged tissues or contaminated cultures.

Sclerotia

During the winter small nodules of firm consistency are formed, known as sclerotia, these are resistance structures that remain in hibernation. These are multicellular flat-convex structures 1-15 mm long by 1.5 mm wide that are formed in decomposed cultures.

The species of the genus Botrytis are highly active even in environments with temperatures below 12 ºC. They generally cause great economic losses in crops stored for a long period of time under refrigerated conditions.

The spores do not directly penetrate the culture tissues, they do so through wounds caused by insect bites, hailstorms or pruning. For this reason, special care must be taken during harvest, since once the fungus penetrates it is difficult to eradicate it.

Botrytis cinerea on vine. Source: davitydave / CC BY (https://creativecommons.org/licenses/by/2.0)

Taxonomy

- Fungi kingdom

- Division: Ascomycota

- Subdivision: Pezizomycotina

- Class: Leotiomycetes

- Order: Helotiales

- Family: Sclerotinicaeae

- Genus: Botrytis

Species

- Botrytis allii: plant pathogen that causes neck rot in stored onions.

- Botrytis cinerea or Botryotinia fuckeliana: species that affects horticultural and fruit crops such as citrus or vineyards.

- Botryotinia convoluta: Botrytis species that affect the rhizomes of ornamental species of the genus Iris.

- Botrytis fabae: species that causes the chocolate stain in bean crops (Vicia faba).

- Botryotinia polyblastis: fungal pathogen that attacks ornamental plants of the genus Narcissus.

Botrytis allii on chives. Source: Jerzy Opioła / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Types (classification)

The fungi belonging to the genus Botrytis can develop in two different ways. Hence, two different types of pathologies are considered:

Botrytis

It is the disease that develops within the host, which is why it is considered difficult to eradicate once installed. In general, it causes the rotting of the internal tissues of the plant, the symptoms are difficult to detect and appear when the disease is very advanced.

Botrytis

The infection is carried out from the outside to the inside, being more frequent in ripe fruits than in tender fruits. It is easier to detect or eradicate, as symptoms can be detected with the naked eye, before they invade internal tissues.

Symptoms

The first symptoms are manifested as dark spots on leaves and flowers, rotten fruit and necrotic tissues in bulbs or stored products. The fungus causes the rotting of the tissues of the affected organ and the progressive decay of the host until causing the death of the plant.

Fruit of Vicia faba affected by Botrytis fabae. Source: Jerzy Opioła / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Plants affected

Viniculture

The species Botrytis cinerea is the causal agent of gray rot in vine crops, causing the grapes to dry out. These symptoms decrease the sugar content and increase the solid elements, which substantially affects the viticultural quality of the crop.

It usually develops in environments with medium temperature and high relative humidity, its incidence being greater in times of rain or when the plant remains wet for a long time. In addition, if the crop presents some type of wound on stems, leaves or flowers, the presence of the pathogen will be unavoidable.

The symptoms can be observed with the naked eye, since there are spots and watery rots of the affected tissues. Over time, the affected surface becomes covered with a gray mold, the mycelium of the fungus, occasionally the plant can die.

Vegetables and fruit trees

The presence of Botrytis on soft fruits, such as tomato, paprika, strawberry, pumpkin or cucumber, even on cut flowers, substantially affects the commercial quality of the crop. Its incidence is favored by poor crop management, either poorly performed pruning or a poor cut during harvest.

When the fungus affects a fruit such as tomato or strawberry, it must be discarded immediately, since they are not considered suitable for human consumption. The best prevention is to keep the crops well ventilated, in this way the humidity is prevented from remaining on the foliage for a long time.

Vicia faba leaves affected with Botrytis fabae. Source: Alexanderlilliehook / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Control

Cultural control

- Use the appropriate sowing density for each crop, avoiding crops that are too dense.

- Under greenhouse conditions control aeration, heating and irrigation frequency.

- Eliminate the affected plants once they are detected.

- Use healing gels when doing some kind of pruning in the crop.

- Use certified seeds.

Biologic control

- Foliar applications with the Trichoderma harzianum fungus in case of detecting the pathogen, it can also be used as a disinfectant for the seeds.

- The use of fungi of the genus Mucor, such as M. corymbilfer, M. mucedo, M. pusillus or M. racemosus, has reported good results in the control of Botrytis during the first stages of infestation.

Chemical control

The application of fungicides to control Botrytis is often ineffective once installed in the crop. However, the application of fungicides based on Iprodione 50% (P / V), Vinclozolin 50% (WP) or Procymidone 50% (WP) is recommended together with a broad spectrum fungicide.

Similarly, it is advisable to carry out preventive treatments before starting flowering and to place fungal pastes on the blackened tissues. However, all chemical treatment must be accompanied by good agronomic management practices to reduce the probability of incidence of this disease.

References

1. Botrytis. (2019). Wikipedia, The Free Encyclopedia. Recovered at: es.wikipedia.org
2. Botrytis (2018) Husqvarna. Recovered at: todohusqvarna.com
3. Garcés de Granada, E., Orozco de Amézquita, M. & Zapata, AC (1999). Phytopathology in flowers. Acta Biológica Colombiana, 4 (2), 5-26.
4. Ramírez, PJ (2017) Considerations for the management of Botrytis. Metroflower. Recovered at: metroflorcolombia.com
5. Romero A., B. & Granados, E. (2018) Botrytis, biology of the pathogen. Syngenta. Recovered in: syngentaornamentales.co
6. Sepúlveda, R. (2015) Botrytis. Technical Sheet No. 9. Recovered at: slideshare.net