Botrytis cinerea is a fungus responsible for gray mold, one of the most economically damaging plant diseases on Earth, causing estimated losses between $10 billion and $100 billion annually across agriculture worldwide.1Crop Protection. Interface of the environment and occurrence of Botrytis cinerea in pre-symptomatic tomato crops It attacks over 400 plant species, from strawberries and tomatoes to grapes and cut flowers, and it is also the only pathogen in agriculture that winemakers sometimes welcome. That split personality, destroyer of harvests on one hand and creator of some of the world’s most prized dessert wines on the other, makes botrytis one of the more fascinating organisms in plant pathology.
What Botrytis Actually Does to a Plant
Botrytis cinerea is a necrotroph, meaning it kills plant cells and then feeds on the dead tissue. It accomplishes this through a combination of weapons. The fungus secretes enzymes that disassemble plant cell walls, breaking apart the structural scaffolding that holds tissue together. Researchers have catalogued roughly 275 of these secreted enzymes in the botrytis genome, including ones that target pectin, hemicellulose, and cellulose, the main building blocks of cell walls.2PubMed Central. Genome-wide transcriptional profiling of Botrytis cinerea genes targeting plant cell walls during infections of different hosts When tested on lettuce leaves, ripe tomato fruit, and grape berries, the fungus expressed a shared core set of about 229 of these enzymes across all three hosts, suggesting it does not need to reinvent its strategy for each crop.
Alongside those enzymes, botrytis produces toxic compounds, most prominently botrydial and botcinic acid. These phytotoxins trigger programmed cell death in plant tissue, essentially tricking the plant into killing its own cells, which then become food for the fungus.3PubMed Central. Loss of virulence of Botrytis cinerea mutants defective in phytotoxin production is restored by modifying inoculation medium The fungus also deploys oxalic acid and reactive oxygen species to overwhelm plant defenses and accelerate cell death.4Journal of General Plant Pathology. Virulence factors of Botrytis cinerea The result is the soft, watery rot and fuzzy gray sporulation that gardeners and farmers recognize instantly.
How Botrytis Hijacks Plant Immunity
One of the more unsettling discoveries about botrytis in recent years is that it does not simply overpower plant defenses with brute force. It also manipulates them at the molecular level. The fungus produces small RNA molecules that enter plant cells and silence specific immunity genes, a process researchers call cross-kingdom RNA interference. Several of these small RNAs have been detected inside infected plants: some shut down genes encoding stress-response enzymes, others target signaling proteins that coordinate the plant’s defense network, and at least one has been shown to silence as many as 15 separate immunity-related genes at once.5PubMed Central. Cross-kingdom small RNA communication between plants and fungal phytopathogens-recent updates and prospects for future agriculture This is not simply an arms race of enzymes against cell walls; the fungus is actively editing the plant’s own defense software.
Plants do fight back. When botrytis enzymes start breaking down cell walls, the resulting fragments can themselves act as alarm signals. These fragments activate defense genes, including one called PAD3, which is required for the production of antimicrobial compounds. In experiments with Arabidopsis, plants lacking PAD3 lost the ability to resist botrytis even when primed with those wall-fragment signals, confirming that this gene plays a critical role in the immune response.6Plant Physiology. Resistance to Botrytis cinerea Induced in Arabidopsis by Elicitors Is Independent of Salicylic Acid, Ethylene, or Jasmonate Signaling But Requires PHYTOALEXIN DEFICIENT3 There is also evidence that the fungus detects specific plant defense chemicals and uses them as cues to ramp up its own detoxification machinery, effectively recognizing its host by “tasting” the plant’s chemical counterattack.7PubMed Central. Botrytis cinerea identifies host plants via the recognition of antifungal capsidiol to induce expression of a specific detoxification gene
The Invisible Stage Before the Rot
One reason botrytis is so frustrating for growers is that it often infects fruit long before any symptoms appear. The fungus can land on an unripe berry or strawberry, begin to penetrate the surface, and then go quiet, persisting between dead cells in a dormant state for weeks or even months. This is called quiescent infection, and it is the main reason produce that looked perfectly healthy at harvest falls apart in storage or on the grocery shelf.
What keeps the fungus dormant is partly the fruit itself. Unripe fruit has higher concentrations of antimicrobial compounds like polyphenols, a firmer cell wall structure, and active defense signaling that holds the pathogen in check. As fruit ripens, those defenses weaken: polyphenol levels drop, cell walls soften, and changes in pH and sugar content create an environment the fungus can exploit. The transition from quiescence to active rot is driven by this shift in the host’s chemistry rather than by any dramatic change in the fungus.8PubMed Central. Quiescence of postharvest pathogens: a fungal inhibition process or an immune response of the unripe host fruit?
Wetness duration matters too. Experiments with sweet cherries showed that shorter periods of moisture after inoculation led to more quiescent infections, while longer wet periods of 18 to 24 hours pushed infections straight into active decay.9PubMed. Identification and Etiology of Visible Quiescent Infections of Monilinia fructicola and Botrytis cinerea in Sweet Cherry Fruit This helps explain why a few rainy days just before harvest can trigger an explosion of gray mold that seems to come out of nowhere.
Noble Rot and the Jekyll-and-Hyde Problem
The same fungus that ruins a crate of strawberries is responsible for Sauternes, Tokaji, and other legendary sweet wines. When botrytis infects ripe white wine grapes under the right conditions, it can produce what winemakers call noble rot instead of destructive gray mold. The berry skin becomes porous, water evaporates, sugars concentrate, and the fungus contributes a suite of aromatic compounds that give the resulting wine its distinctive honeyed, apricot-like character. Molecules like phenylacetaldehyde, furaneol, and γ-nonalactone are positively associated with noble-rot grapes, while certain fermentative esters decrease.10Food Chemistry. Effects of noble rot on must composition and aroma profile of Amarone wine produced by the traditional grape withering protocol
What determines which outcome you get is not a special strain of botrytis. Genetic studies have found no consistent differences between populations associated with noble rot and those causing gray mold. Instead, it comes down to weather. Noble rot develops when humid mornings encourage infection but dry, sunny afternoons allow berries to dehydrate slowly rather than collapse into mush.11PubMed Central. The ‘Dr Jekyll and Mr Hyde fungus’: noble rot versus gray mold symptoms of Botrytis cinerea on grapes Berries exposed to noble-rot-inducing conditions dehydrate gradually and accumulate higher levels of soluble solids but actually harbor less fungal biomass compared to berries undergoing straight bunch rot.12Physiological and Molecular Plant Pathology. Distinct volatile signatures of bunch rot and noble rot This means the “noble” in noble rot is really about restraint: a slow, controlled infection under dry conditions versus an aggressive takeover under wet ones.
On the chemical side, noble rot also reshapes the polyphenol profile of grapes. Total polyphenols can drop by up to 40 percent as infection advances, while certain compounds like catechin and epicatechin actually increase, and new ones appear. The flavonol myricetin, not previously reported in white grapes, has been found only in heavily botrytized berries, suggesting the fungus either synthesizes it or triggers the grape to produce it.13European Food Research and Technology. Physico-chemical properties of botrytised Chenin blanc grapes to assess the extent of noble rot Humidity-controlled postharvest withering can even be used to intentionally induce noble rot on harvested grape bunches, giving winemakers more control over the process than relying solely on field conditions.14PubMed Central. The Induction of Noble Rot (Botrytis cinerea) Infection during Postharvest Withering Changes the Metabolome of Grapevine Berries (Vitis vinifera L., cv. Garganega)
Why Fungicides Keep Losing Ground
Botrytis has a remarkable capacity to develop resistance to chemical fungicides, and multidrug resistance (where a single isolate shrugs off two or more unrelated fungicide classes) is increasingly common in field populations. The mechanisms are well studied. One major route involves mutations in a transcription factor called Mrr1 that ramps up production of an efflux pump, essentially a molecular vacuum cleaner that ejects fungicide molecules from the cell before they can do damage. A second route involves a rearrangement in the promoter region of another transporter gene, caused by the insertion of a jumping genetic element. Both mechanisms result in the fungus actively pumping out whatever chemical it encounters.15PLoS Pathogens. Fungicide-Driven Evolution and Molecular Basis of Multidrug Resistance in Field Populations of the Grey Mould Fungus Botrytis cinerea
What makes this even more troubling is that the fungus does not necessarily need fungicide exposure to develop these resistance mechanisms. Research has shown that exposure to natural plant defense compounds, like resveratrol and other secondary metabolites, can upregulate the same efflux-pump genes that confer resistance to synthetic fungicides. After just 15 generations of growth on these plant compounds, botrytis strains showed decreased sensitivity to multiple fungicides including widely used products like boscalid and fludioxonil.16PubMed Central. Multidrug resistance of Botrytis cinerea associated with its adaptation to plant secondary metabolites In other words, the fungus’s normal arms race with its host plants may be pre-adapting it to resist our chemicals before it ever encounters them in a spray tank. The practical consequence: rotating fungicide classes, the standard recommendation, helps slow resistance but cannot eliminate it.17PubMed Central. Understanding Efflux-Mediated Multidrug Resistance in Botrytis cinerea for Improved Management of Fungicide Resistance
Biological Control Alternatives
Given the resistance problem, there is growing interest in using living organisms to fight botrytis instead of, or alongside, chemical sprays. One of the most promising groups of biocontrol agents is Bacillus velezensis, a bacterium found naturally in soil. Multiple strains have shown strong activity against gray mold in laboratory and greenhouse trials. One strain achieved over 78 percent biocontrol efficiency against gray mold on tomato and pepper leaves and fruit.18PubMed Central. A novel biocontrol agent Bacillus velezensis K01 for management of gray mold caused by Botrytis cinerea Another showed roughly 75 percent inhibition of the fungus and was effective against several other crop pathogens as well. That strain worked partly by damaging the integrity of botrytis cell membranes and partly by switching on the tomato plant’s own defense genes.19Postharvest Biology and Technology. Biocontrol performance of a novel Bacillus velezensis L33a on tomato gray mold and its complete genome sequence analysis
Another avenue involves mycoviruses, viruses that infect fungi. Some mycoviruses reduce the virulence of botrytis without killing it outright. One such virus suppressed the formation of infection cushions, the specialized structures the fungus uses to breach plant surfaces, and downregulated the genes associated with building them. Interestingly, if the virus-infected fungus was inoculated directly into a wound, bypassing the need for an infection cushion, its virulence was fully restored, confirming that the virus specifically disrupts the penetration step rather than broadly weakening the fungus.20PubMed Central. Two Novel Hypovirulence-Associated Mycoviruses in the Phytopathogenic Fungus Botrytis cinerea: Molecular Characterization and Suppression of Infection Cushion Formation Whether mycoviruses could be deployed as practical biocontrol tools in the field remains an open question, but the specificity is appealing.
RNA Sprays as a Chemical-Free Fungicide
Perhaps the most futuristic approach to botrytis management is spray-induced gene silencing, or SIGS. The idea is to spray plants with double-stranded RNA molecules designed to match and shut down essential genes in the fungus. Botrytis is an especially good candidate for this technology because it is unusually efficient at absorbing RNA from its environment.21PubMed Central. Spray-induced gene silencing for disease control is dependent on the efficiency of pathogen RNA uptake Not all pathogens can do this; when tested alongside other fungi and an oomycete, botrytis was among those with the highest uptake efficiency, and the correlation between uptake and disease suppression was strong.
Recent work has pushed this concept closer to practical use. RNA targeting the Mrr1 gene, the same transcription factor that drives multidrug resistance, suppressed disease for up to 14 days after a single foliar spray. It worked against both fungicide-sensitive and multidrug-resistant isolates, and the protection held on both leaves and apple fruit.22PubMed. Spray-Induced Gene Silencing Targeting the Transcription Factor Bcmrr1: A Sustainable RNAi-Based Strategy to Control Botrytis cinerea and Overcome Multidrug Resistance The elegance of this approach is that it turns the fungus’s own resistance machinery against it: the gene that makes botrytis resistant to fungicides becomes the target of the RNA spray. A major remaining challenge is that naked RNA degrades quickly outdoors. Researchers are developing artificial nanovesicles and other delivery systems to protect the RNA from UV light and rain long enough for it to work.23PubMed Central. Artificial nanovesicles for dsRNA delivery in spray-induced gene silencing for crop protection
Genetic Diversity Across Hosts
Botrytis is not a single uniform population. Its genome carries mobile genetic elements, jumping segments of DNA that shuffle around and create variation between strains. One study of 334 isolates collected from grapes, strawberries, tomatoes, cucumbers, kiwifruit, and apples found marked differences in which mobile elements each population carried. On tomato, cucumber, grape, and strawberry, strains carrying both major mobile elements dominated. On kiwifruit and apple, strains lacking both elements were more common.24PubMed. Differences in Frequency of Transposable Elements Presence in Botrytis cinerea Populations from Several Hosts in Greece Whether these genetic differences translate to meaningful differences in aggressiveness or fungicide sensitivity on different crops is still being sorted out, but the pattern suggests that botrytis populations are not freely interchangeable across hosts despite the fungus’s enormous overall host range.
Deeper genome comparisons between strains from grapevine and tomato have found differences not just in mobile elements but also in accessory chromosomes and small RNA repertoires.25Peer Community Journal. Botrytis cinerea strains infecting grapevine and tomato display contrasted repertoires of accessory chromosomes, transposons and small RNAs Grapevine strains, for instance, had a greater number of mobile-element subfamilies and higher overall genome coverage by these elements than tomato strains. This kind of structural variation could influence how quickly different botrytis populations evolve resistance to fungicides or adapt to new hosts.
What Climate Change May Mean for Botrytis
Because botrytis thrives in cool, humid conditions, you might expect a warming climate to simply push it out. The reality is more complicated. Modeling of the fungus’s suitable range in China under future climate scenarios found that the center of its distribution did not shift much. High-suitability areas actually shrank, but medium-suitability areas expanded, meaning the fungus’s range could become more diffuse rather than smaller.26PubMed Central. Changes in the Distribution of Botrytis cinerea Pers. Fr. In China Under Climate Change The key environmental drivers were not straightforward temperature averages but rather variables like temperature stability, rainfall seasonality, and precipitation during the coldest quarter. Botrytis is sensitive to the pattern of wet and dry periods, not just the thermometer. Regions that become warmer but also wetter during critical crop stages could see more gray mold, not less.
Keeping Botrytis Off Your Produce at Home
For consumers, the most relevant encounter with botrytis is the fuzzy gray mold that appears on strawberries, raspberries, and grapes in the fridge. Because the fungus often arrives as a latent infection already inside the fruit, surface washing alone will not prevent it. Temperature is the single biggest lever you have. Keeping berries consistently cold, ideally near 0°C (32°F), slows both the fruit’s ripening and the fungus’s growth. Fluctuations in temperature and humidity during storage accelerate spoilage; the cold chain matters more than any single moment of refrigeration.27Food Packaging and Shelf Life. Predicting quality attributes of strawberry packed under modified atmosphere throughout the cold chain Sorting out any visibly moldy fruit immediately helps too, since botrytis sporulates aggressively and the spores spread quickly to adjacent fruit in a closed container. Proper airflow around the fruit, rather than sealing it in a tight bag, reduces the moisture buildup that favors fungal growth. None of this guarantees mold-free berries, but it buys meaningful time.