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Botrytis cinerea is a necrotrophic fungus that affects many plant species, including wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or "gray mold".
The fungus gives rise to two different kinds of infections on grapes. The first, grey rot, is the result of consistently wet or humid conditions, and typically results in the loss of the affected bunches. The second, noble rot, occurs when drier conditions follow wetter, and can result in distinctive sweet , such as Sauternes, the Aszú of Tokaji, or Grasă de Cotnari. The species name Botrytis cinerea is derived from the Latin for "grapes like ashes"; the "grapes" refers to the bunching of the fungal spores on their Conidium, while "ashes" refers to the greyish colour of the spores en masse. The fungus is usually referred to by its anamorph (asexual form) name, because the sexual phase is rarely observed. The teleomorph (sexual form) is an ascomycete, Botryotinia fuckeliana, also known as Botryotinia cinerea (see taxonomy box).
Plants can produce localized lesions when a pathogen attacks. An oxidative burst causes hypersensitive cell death called a hypersensitive response (HR). This soft rot can trigger HR to assist in colonization. Botrytis cinerea, as a necrotrophic pathogen, exploits the dead tissue for its pathogenicity or its ability to cause disease. Susceptible plants cannot use the HR to protect against B. cinerea.
Gliocladium roseum is a fungal parasite of B. cinerea.
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 mutation of the transcription factor mrr1, which in turn confer a multiple fungicide resistance phenotype known as . An even higher overexpression yields mrr1 composed partly of , yielding MDR1h phenotypes with even more anilinopyrimidine- and phenylpyrrole- resistance.
Standing water on plant leaf surfaces provides a place for spores to germinate.Physiological Aspects of Resistance to Botrytis cinerea. Elad, Y. and Evensen, K.. Publication 3 April 1995[1] 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.
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.
A low pH is preferred by the gray mold to perform well. B. cinerea can acidify its environment by secreting , like oxalic acid. By acidifying its surroundings, cell wall degrading enzymes (CWDEs) are enhanced, plant-protection enzymes are inhibited, closure is deregulated, and pH signaling is mediated to facilitate its pathogenesis.
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 Sauternes, largely due to the vineyard's susceptibility to noble rot.
Botrytis complicates the fermentation process during winemaking. 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.
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 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.
The infection also affects rhubarb, , white meadowfoam, western hemlock,Van Eerden, E. (1974, August). Growing season production of western conifers. In Proc. North American Containerized Forest Tree Seedling Symp., Denver, Colorado (pp. 93-103) Douglas-fir,Brix, Holger, and H. Barker. "Rooting studies of western hemlock cuttings." (1975). cannabis, (2017). 9783319545639, Springer International. ISBN 9783319545639 and Lactuca sativa. UV-C treatment against B. cinerea was investigated by Vàsquez et al., 2017. They find it increases phenylalanine ammonia-lyase activity and production of phenols. This in turn decreases L. sativas susceptibility. Potassium bicarbonate-based fungicide may be used.
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.
Not planting 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.
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.
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.
Biological controls or microbial antagonists 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). Trichoderma species especially, have been shown to control gray mold.
Multiple fungicide resistance is a problem in many production areas.
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