Botrytis cinerea

"Botrytis" is derived from the Ancient Greek botrys (βότρυς) meaning "grapes",[2] combined with the New Latin suffix -itis for disease.

Conidiophore

Petri dish with a ring of visible sclerotia (dark brown balls)

Botrytis cinerea is characterized by abundant hyaline conida (asexual spores) borne on grey, branching tree-like conidiophores. The fungus also produces highly resistant sclerotia as survival structures in older cultures. It overwinters as sclerotia or intact mycelia, both of which germinate in spring to produce conidiophores. The conidia, dispersed by wind and by rain-water, cause new infections. B. cinerea performs an asexual cycle over the summer season.

Different strains show considerable genetic variability.

Gliocladium roseum is a fungal parasite of B. cinerea.[9]

The hypothetical protein BcKMO was shown to positively regulate growth and development. It showed a great similarity to the kynurenine 3-monooxygenase encoding gene in eukaryotes.

Overexpression of the gene atrB produces altered versions of the transcription factor mrr1, which in turn confer a multiple fungicide resistance phenotype known as MDR1.[5] An even higher overexpression yields mrr1 composed partly of Δ497V/L, yielding MDR1h phenotypes with even more anilinopyramidine- and phenylpyrrole- resistance.[5]

Gray mold favors moist, humid, and warm environmental conditions between 65–75 °F (18–24 °C).[10] Temperature, relative humidity, and wetness duration produce a conducive environment that is favorable for inoculation of mycelium or conidia.[11] Controlled environments, such as crop production greenhouses, provide the moisture and high temperatures that favor the spreading and development of the pathogen B. cinerea.

Standing water on plant leaf surfaces provides a place for spores to germinate.[12] Humid conditions can result from improper irrigation practice, plants placed too close together, or the structure of the greenhouse not allowing for efficient ventilation and air flow. Ventilation at night significantly reduces the incidence of gray mold.[13]

Melanized sclerotium allows B. cinerea to survive for years in the soil. Sclerotia and the asexual conidia spores contribute to the widespread infection of the pathogen.[14]

A low pH is preferred by the gray mold to perform well. B. cinerea can acidify its environment by secreting organic acids, like oxalic acid.[14] By acidifying its surroundings, cell wall degrading enzymes (CWDEs) are enhanced, plant-protection enzymes are inhibited, stomatal closure is deregulated, and pH signaling is mediated to facilitate its pathogenesis.[14]

Manifesting as noble rot on Riesling

In the Botrytis infection known as "noble rot" (pourriture noble in French, or Edelfäule in German), the fungus removes water from the grapes, leaving behind a higher percent of solids, such as sugars, fruit acids and minerals. This results in a more intense, concentrated final product. The wine is often said to have an aroma of honeysuckle and a bitter finish on the palate.

A distinct fermentation process initially caused by nature, the combination of geology, climate and specific weather led to the particular balance of beneficial fungus while leaving enough of the grape intact for harvesting. The Chateau d'Yquem is the only Premier Cru Supérieur, largely due to the vineyard's susceptibility to noble rot.

Botrytis complicates winemaking by making fermentation more complex. Botrytis produces an anti-fungal compound that kills yeast and often results in the fermentation stopping before the wine has accumulated sufficient levels of alcohol.[15]

Botrytis bunch rot is another condition of grapes caused by B. cinerea that causes great losses for the wine industry. It is always present on the fruitset, however, it requires a wound to start a bunch rot infection. Wounds can come from insects, wind, accidental damage, etc. To control botrytis bunch rot there are a number of fungicides available on the market. Generally, these should be applied at bloom, bunch closure and veraison (the most important being the bloom application). Some winemakers are known to use the German method of fermentation and prefer having a 5% bunch rot rate in their grapes and will usually hold the grapes on the vine a week longer than normal.

Botrytis cinerea affects many other plants.

Botrytis cinerea mold on grapes may cause "winegrower's lung", a rare form of hypersensitivity pneumonitis (a respiratory allergic reaction in predisposed individuals).

Mycoviruses

Botrytis cinerea not only infects plants, it also hosts several mycoviruses itself (see the table/image).

A range of phenotypic alterations due to the mycoviral infection have been observed from symptomless to mild impact, or more severe phenotypic changes including reduction in pathogenicity, growth/suppression of mycelia, sporulation and sclerotia production, formation of abnormal colony sectors (Wu et al., 2010[22]) and virulence.

Botrytis cinerea can be managed through cultural, chemical, and biological practices.

There are no resistant species to the gray mold rot. Gray mold can be culturally controlled by monitoring the amount and timing of fertilizer applications to reduce the amount of fruit rot. Excessive application of nitrogen will increase the incidence of disease while not improving yields.[6]

Not planting cultivars that have an upright or dense growth habit can reduce disease as these limit airflow and are favorable for the pathogen. Spacing of plants so they are not touching will increase airflow allowing the area to dry out and reduce the spread of disease. Pruning or purposeful removal of diseased, dead, or overgrown limbs on a regular schedule can also help to improve air movement.[7]

Sanitation by removing dead or dying plant tissue in the fall will decrease inoculum levels as there is no debris for the sclerotium or mycelia to overwinter. Removing debris in the spring will remove inoculum from the site. Disposal of berries during harvest that have signs and symptoms of gray mold will reduce inoculum for the following year.

Biochar, a form of charcoal, can be applied as a soil amendment to strawberry plants to reduce the severity of the fungal disease by stimulating defense pathways within the plant.[23]

Gray mold can be chemically controlled with well-timed fungicide applications starting during the first bloom. Timing can reduce the chance of resistance and will save on costs.[6]

Biological controls or microbial antagonists[24] used for disease suppression, have been successfully used in Europe and Brazil in the form of fungi-like Trichoderma harzianum Rifai and Clonostachys rosea f. rosea Bainier (syn. Gliocladium roseum).[23] Trichoderma species especially, have been shown to control gray mold.

Multiple fungicide resistance is a problem in many production areas.[5]

• Botrydial

Wikimedia Commons has media related to Botrytis cinerea.

• Genome information for Botrytis cinerea
• Genome analysis of Botrytis cinerea
• Choquer M, Fournier E, Kunz C, et al. (December 2007). "Botrytis cinerea virulence factors: new insights into a necrotrophic and polyphageous pathogen". FEMS Microbiol. Lett. 277 (1): 1–10. doi:10.1111/j.1574-6968.2007.00930.x. PMID 17986079.
• TheWineDoctor.com
• Büttner P, Koch F, Voigt K, et al. (May 1994). "Variations in ploidy among isolates of Botrytis cinerea: implications for genetic and molecular analyses". Curr. Genet. 25 (5): 445–50. doi:10.1007/BF00351784. PMID 8082191. S2CID 10886741.
• Vallejo, I.; Santos, M.; Cantoral, J. M.; Collado, I. G.; Rebordinos, L. (2004). "Chromosomal polymorphism in Botvytis cinerea strains". Hereditas. 124: 31–38. doi:10.1111/j.1601-5223.1996.00031.x.
• Staats M, van Baarlen P, van Kan JA (February 2005). "Molecular phylogeny of the plant pathogenic genus Botrytis and the evolution of host specificity". Mol. Biol. Evol. 22 (2): 333–46. doi:10.1093/molbev/msi020. PMID 15496556.