In the vast network of interactions that constitute agricultural ecosystems, the fungus Botrytis cinerea emerges as an enemy of farmers and products around the world. Popularly known as gray rot fungus, this filamentous pathogen wreaks havoc on a wide variety of crops, from fruits and vegetables to ornamentals. In this blog post, we will explore in detail the key aspects related to Botrytis: from its biology and life cycle, to the damage it causes, to the symptoms it causes, to the hosts it affects, the challenges associated with the development of resistance, through to the treatment and control strategies available to mitigate its impact on agriculture.
# # # Biology and life cycle of Botrytis cinerea # # #
Botrytis cinerea is an ascomycete fungus belonging to the Sclerotiniaceae family. It is a saprophytic (feeds on dead plant matter) species commonly found in soil and decaying plant matter. Despite its saprophytic nature, Botrytis cinerea is also an opportunistic pathogen capable of infecting a wide range of plants, especially under conditions of high humidity and moderate temperatures.
The life cycle of Botrytis cinerea is complex and includes both asexual and sexual reproduction. Under favorable conditions of humidity and temperature, during its asexual phase, Botrytis cinerea produces asexual spores called conidia. These conidia are small, single-celled, and contained in specialized structures called conidiophores. Conidiophores are branches of mycelium that emerge from lesions on infected plants and release conidia into the environment, where they can be carried by wind or water to new host plants (giving them that fuzzy appearance). Once inside the plant, the fungus grows and produces new conidial structures, which in turn generate more secondary infections.
In its sexual phase and under unfavorable conditions such as drought or cold, Botrytis produces complex reproductive structures called sclerotia. Sclerotia are hard, dark-colored, very resilient structures that enable long-term survival. These sclerotia can persist in soil or dead plant tissue for long periods of time and serve as a source of inoculum for future infections.
The sclerotia contain sex cells called ascospores. These ascospores are released into the environment when the sclerotia decompose, contributing to the dispersal and spread of the fungus.
# # # Environmental conditions # # #
Temperature: Botrytis cinerea thrives in moderate temperatures, with an optimal growing range between 15°C and 25°C. However, it can survive and grow in a wider temperature range, from 0°C to around 35°C. Lower temperatures slow the growth of the fungus, while higher temperatures can encourage sporulation and the spread of the disease.
Behavior of Botrytis with respect to temperature:
Formation of sclerotia: 11°C – 15°C.
Germination: 20°C – 25°C.
Optimal development: 18°C - 23°C.
Growth: 0°C - 35°C.
Relative Humidity: Relative humidity of the air is a crucial factor for the development of Botrytis cinerea. The disease tends to be more severe in conditions of high humidity, particularly when relative humidity exceeds 90%, with 95% being optimal humidity. The formation of water droplets on plant surfaces or in the soil can increase the incidence of the disease by providing a favorable environment for the growth of the fungus.
Foliar humidification: Foliar humidification, such as dew or rain, can promote the germination of Botrytis cinerea spores and the penetration of the fungus into plant tissues. Therefore, plants that remain wet for long periods of time are more susceptible to infections.
# # # Damage and Symptoms: How to Identify Infections Caused by Botrytis cinerea# # #
Damage caused by Botrytis cinerea can be devastating to agricultural crops and can manifest in a variety of ways, depending on the host and environmental conditions. Below are some of the most common symptoms associated with Botrytis infection:
Leaves
Gray rot is the most characteristic symptom of Botrytis cinerea infection and the main sign of its presence. It initially appears as watery spots on the underside of leaves, near the tips, which quickly become brown and covered with grayish mold. Over time, the lesions expand and become soft and slimy, leading to complete breakdown of the affected tissues.
Stems
Botrytis can develop necrotic spots on infected stems. These lesions usually start as small light brown spots that can grow and coalesce to form larger areas of dead tissue. As is the case on leaves, grayish fungal growth may be seen on infected stems. This gray rot is the typical characteristic of the presence of Botrytis cinerea. As the infection progresses, affected stems may begin to wilt and rot, weakening the plant and affecting its ability to transport water and nutrients.
Wilting of flowers and buds
Botrytis cinerea can infect flowers and buds, causing them to wilt prematurely. This symptom significantly affects crop yield and quality, leading to significant reductions in production.
Decomposition of fruits and vegetables
In stored fruits and vegetables, Botrytis cinerea can cause tissue decomposition due to the enormous amount of enzymes it secretes into infected tissues with lytic activities, hence the watery appearance at the points of infection .
# # # Who does Botrytis cinerea infect? # # #
Botrytis cinerea does not discriminate between crops and can affect a wide variety of plants, including fruits, vegetables, cereals, legumes, ornamentals and woody crops. Some of the most common hosts of Botrytis cinerea include:
Fruit
Grapes: Botrytis cinerea is particularly problematic in vineyards, where it can cause grape clusters to rot, reducing wine yield and quality.
Strawberries: Strawberries are susceptible to Botrytis cinerea infection, especially during periods of high humidity and rain.
Raspberries: Raspberries are vulnerable to gray rot, which can affect fruit in the field and during storage.
Vegetables
Tomatoes: Botrytis cinerea can infect tomato fruits, as well as leaves and stems, causing significant crop damage.
Peppers: Peppers are susceptible to infection by Botrytis cinerea, which can cause fruit rot and plant wilting.
Lettuce: Lettuce can be affected by Botrytis cinerea, especially in conditions of high humidity and poor air circulation.
Ornamental plants
Roses: Botrytis cinerea can infect rose buds, causing them to wilt prematurely and reduce flower quality.
Chrysanthemums: Chrysanthemums are susceptible to infection by Botrytis cinerea, which can cause stem and leaf rot.
Gerberas: Gerberas can be affected by gray rot, which can reduce the longevity of the flowers and affect their marketability.
# # # Botrytis cinerea Treatments and Control Strategies # # #
Integrated pest and disease management is essential to effectively control Botrytis cinerea. Below we present some treatment and control strategies that can help lessen the impact of the disease:
Cultural practices
Ø Promote air circulation: Maintaining good air circulation around plants can help reduce moisture on the surface of leaves and fruits, reducing the incidence of Botrytis cinerea.
Ø Removal of infected plant material: Prompt removal of infected plant material can help prevent the spread of disease and reduce the amount of inoculum available for new infections.
Ø Avoid excessive humidity: Avoiding excessive watering and ensuring adequate soil drainage can help reduce humidity in the environment, making it difficult for Botrytis cinerea to develop and spread.
Ø Promotion of air circulation: Use of seeds with a health analysis certificate
Ø Planting density: Planting density can also influence the incidence of Botrytis cinerea. Plants close together may experience poor air circulation and higher relative humidity, which encourages fungal development. Therefore, proper plant spacing can help reduce the risk of infection.
Use of fungicides
Ø Selection of appropriate treatment
Ergosterol Synthesis Inhibitors: Include four groups of fungicides: triazole amines, hydroxyanilides, and thiocarbamate that affect ergosterol biosynthesis in pathogen cells.
Amino acid and protein synthesis inhibitors: Includes cyprodinil, pyrimethanil, and mepanipyrim.
External Quinone Inhibitor: Inhibits electron transfer at the Qo site in mitochondrial complex III.
Succinate dehydrogenase inhibitors: These include molecules such as Boscalid, Floupyram and Fluxapyroxad. They affect the enzyme succinate dehydrogenase, in the metabolic pathway of respiration.
Multisite chemical activity: It has various mechanisms of action, as it can simultaneously interfere with different organelles and physiological processes in fungal cells, including: Folpet, Captan, Sulfur, among others.
Ø Product rotation: Rotating the use of fungicides with different modes of action can help prevent the development of resistance in Botrytis cinerea populations. It is important to alternate between different classes of fungicides and not rely too heavily on any one chemical.
Ø Preventive application: Preventive application of fungicides, before disease symptoms appear, can help protect crops against Botrytis cinerea infection. It is important to follow the dosage and frequency of application recommendations specified on the product label.
Biocontrol agents
It consists of the use of microorganisms and organic extracts that usually colonize plant tissue wounds using all available nutrients, making it difficult for spores of other pathogenic organisms to germinate.
Ø Trichoderma spp. : Certain species of Trichoderma, such as Trichoderma harzianum and Trichoderma atroviride, are known for their ability to colonize soil and plant tissues, competing with Botrytis cinerea for resources and space. Additionally, these fungi can produce enzymes that degrade the cell walls of the pathogenic fungus, thereby interfering with its growth and spread.
Ø Bacillus spp. : Certain species of bacteria in the genus Bacillus, such as Bacillus subtilis and Bacillus amyloliquefaciens, produce antimicrobial compounds that can inhibit the growth of Botrytis cinerea. These bacteria can also colonize the surface of plants, forming a protective layer that makes it difficult for the pathogenic fungus to enter.
Ø Gliocladium spp. : Gliocladium species, such as Gliocladium roseum, are antagonistic fungi that can compete with Botrytis cinerea for space and nutrients. Additionally, some strains of Gliocladium spp. They produce antifungal metabolites that can inhibit the growth of the pathogen.
Ø Pseudomonas spp. : Some strains of Pseudomonas bacteria, such as Pseudomonas fluorescens, produce antibiotic metabolites and enzymes that can inhibit the growth of Botrytis cinerea. These bacteria can also induce defense responses in host plants, thereby strengthening their resistance to infections.
# # # Development of resistance and challenges in controlling Botrytis cinerea # # #
One of the main challenges in managing Botrytis cinerea is the development of fungicide resistance. Continued excessive use of fungicides has led to the development of strains of Botrytis cinerea resistant to several classes of chemicals. In addition, continued pressure and the banning of certain fungicides are leading to the emergence of resistance.
These resistances represent a major challenge for disease control, because they limit the effectiveness of conventional treatments and increase the difficulty of controlling the disease. To address this problem, it is essential to implement integrated pest and disease management strategies that reduce selection pressure on fungal populations and promote genetic diversity within pathogen populations.
The main causes of the appearance of resistance in Botrytis are:
Excessive or inappropriate use of plant protection products: Frequent and repeated application of the same plant protection product or the use of sublethal doses can select populations of resistant fungi.
Monocultures and intensive agricultural practices: Agricultural systems that rely heavily on monocultures and intensive agricultural practices can increase selection pressure for resistance to plant protection products.
Lack of rotation of modes of action: If chemicals with the same mode of action are constantly used, this can promote the development of resistance in fungal populations.
Capacity for rapid adaptation: Botrytis cinerea has a great capacity for adaptation and development of resistance to fungicides due to its genetic variability and its capacity to generate mutations.
Horizontal transfer of resistance genes: Horizontal transfer of fungicide resistance genes between different fungal populations or even between species can contribute to the development and spread of resistance.
Resistance mechanisms: Botrytis cinerea can develop various fungicide resistance mechanisms, such as overexpression of detoxification genes, reduction of fungicide accumulation inside the cell, and modification of fungicide sites of action.
Tolerance to sublethal doses: Botrytis cinerea populations can develop tolerance to sublethal doses of fungicides, which may allow their survival and reproduction in the presence of the fungicide.
Inadequate resistance management: Failure to implement resistance management practices, such as rotating modes of action, applying fungicides in mixtures or sequences, and using integrated control strategies antiparasitic, can contribute to the development and spread of resistance.
How can we avoid it:
Fungicide rotation: Alternate between different chemical groups of fungicides to avoid continued selective pressure on the Botrytis cinerea population.
Use of fungicides in mixture or sequence: Combining different fungicides with different modes of action or alternating between them in sequence can reduce the risk of emergence of resistant strains.
Surveillance and early detection of resistance: Perform fungicide susceptibility testing on Botrytis cinerea populations to detect the presence of resistant strains and adjust management strategies accordingly
Integrated use of control strategies: Implement integrated pest management practices that include preventative, cultural, biological and chemical measures to reduce selective pressure on the Botrytis cinerea population and minimize the risk of resistance.
Promote biodiversity: Encouraging the genetic diversity of Botrytis cinerea in the agricultural environment by conserving natural habitats, crop rotation and promoting sustainable agricultural systems can help reduce the selection of resistant strains.
Education and training: Education and training of farmers on integrated pest management practices and appropriate use of fungicides can contribute to more effective and responsible application of plant protection products.
# # # In vitro resistance analysis: importance and advantages # # #
In vitro resistance testing plays a crucial role in the management and control of pathogens such as Botrytis cinerea in agriculture. These tests allow researchers and farmers to evaluate the sensitivity of pathogen populations to different classes of fungicides, identify resistant strains and develop more effective management strategies. In this section, we will explore the importance and benefits of in vitro resistance analysis in the context of combating Botrytis cinerea.
Importance of in vitro resistance analysis
Detect emerging resistance: In vitro resistance analyzes allow early detection of the presence of strains of Botrytis cinerea resistant to specific fungicides. This is crucial to preventing the spread of resistance and taking preventative measures before resistance becomes a widespread problem.
Evaluate the effectiveness of fungicides: In vitro resistance analyzes provide precise information on the effectiveness of different fungicides against populations of Botrytis cinerea. This allows farmers to select the most effective products to combat diseases and optimize the use of available resources.
Develop integrated management strategies: Knowing the sensitivity profile of Botrytis cinerea populations to fungicides allows researchers and farmers to develop integrated management strategies that combine different control methods, such as cultural practices, use of fungicides and biocontrol, to reduce selection pressure and prevent the development of resistance.
Advantages of in vitro resistance analysis
Reduced costs and losses: By identifying resistant strains of Botrytis cinerea early, in vitro resistance testing helps avoid the unnecessary use of ineffective fungicides, thereby reducing production costs and minimizing economic losses associated with the disease.
Optimizing fungicide use: By knowing the sensitivity of Botrytis cinerea populations to different fungicides, farmers can select and rotate products more effectively, thereby extending the shelf life of fungicides and reducing the risk of resistance development.
Improve control effectiveness: In vitro resistance testing allows farmers to refine their control strategies, thereby improving the control effectiveness of Botrytis cinerea and reducing the incidence and severity of the disease in crops.
Analyzes of resistance to phytosanitary products carried out by specialized laboratories are valuable tools in the management and control of pathogens such as Botrytis cinerea in agriculture. Resistance analyzes such as those carried out at the ZeriMar Laboratory provide crucial information on the sensitivity of pathogen populations to different fungicides, allowing farmers, technicians and agronomists to develop more effective and sustainable management strategies to protect crop health and ensure the production.
Botrytis cinerea poses a constant threat to agriculture worldwide, but with good management and implementation of prevention and control measures, it is possible to reduce its impact and protect crop health. It is essential to adopt an integrated approach combining cultural practices, use of fungicides, resistance analysis and use of biocontrol agents to minimize the spread and damage caused by this pathogen. At the same time, it is important to continue research and development of new tools and technologies for the analysis of Botrytis cinerea resistance.
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