Botrytis cinerea

Botrytis cinerea is a necrotrophic (feeding on dead tissue) 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 dessert wines, 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 conidiophores, 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).

Etymology

Botrytis is derived from the Ancient Greek botrys (βότρυς) meaning "grapes", combined with the Neo-Latin suffix -itis for disease. Botryotinia fuckeliana was named by mycologist Heinrich Anton de Bary in honor of another mycologist, Karl Wilhelm Gottlieb Leopold Fuckel. Synonyms for the sexual stage are:

Botrytis fuckeliana N.F. Buchw., (1949)
Botrytis gemella (Bonord.) Sacc., (1881)
Botrytis grisea (Schwein.) Fr., (1832)
Botrytis vulgaris (Pers.) Fr., (1832)
Haplaria grisea Link, (1809)
fuckeliana de Bary
Phymatotrichum gemellum Bonord., (1851)
Polyactis vulgaris Pers., (1809)
Sclerotinia fuckeliana (de Bary) Fuckel, (1870)

Hosts and symptoms

Hosts

The disease, gray mold, affects more than 200 dicotyledonous plant species and a few monocotyledonous plants found in temperate and subtropical regions, and potentially over a thousand species. Serious economic losses can be a result of this disease to both field and greenhouse grown crops. The causal agent, Botrytis cinerea can infect mature or senescent tissues, plants prior to harvest, or seedlings. There is a wide variety of hosts infected by this pathogen including protein crops, fiber crops, oil crops, and horticultural crops. Horticultural crops include vegetables (examples are chickpeas, lettuce, broccoli, and beans) and small fruit crops (examples are grape, strawberry, raspberry, and blackberry Twigs infected with gray mold will die back. Blossoms will cause fruit drop and injury, such as ridging on developing and mature fruit. Symptoms are visible at wound sites where the fungus begins to rot the plant. Gray masses with a velvety appearance are conidia on the plant tissues are a sign of plant pathogen. 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.

Biology

thumbnail|right|Conidiophore

thumbnail|right|[[Petri dish with a ring of visible sclerotia (dark brown balls)]]

Botrytis cinerea is characterized by abundant hyaline conidia (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.

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 ' produces altered versions of the transcription factor mrr1, which in turn confer a multiple fungicide resistance phenotype known as . Temperature, relative humidity, and wetness duration produce a conducive environment that is favorable for inoculation of mycelium or conidia. 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. 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 organic acids, like oxalic acid.

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.

Horticulture

Botrytis cinerea affects many other plants.

Strawberries

It is economically important on soft fruits such as strawberries and bulb crops.

thumb|Moldy strawberries

Other plants

thumb|right|Botryotinia fuckeliana on a [[Belle de Boskoop|Goudreinet apple]]

In greenhouse horticulture, Botrytis cinerea is well known as a cause of considerable damage in tomatoes.

The infection also affects rhubarb, snowdrops, white meadowfoam, western hemlock, Douglas-fir, cannabis, 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 phenolics. This in turn decreases L. sativas susceptibility.) and virulence.

Management

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.

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.

References

External links

Genome information for Botrytis cinerea
Genome analysis of Botrytis cinerea
TheWineDoctor.com