Botryotinia porri (Botrytis rot of garlic)
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Risk of Introduction
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Means of Movement and Dispersal
- Plant Trade
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Botryotinia porri (H.J.F. Beyma) Whetzel
Preferred Common Name
- Botrytis rot of garlic
Other Scientific Names
- Botrytis porri N.F. Buchw.
- Sclerotinia porri H.J.F. Beyma
International Common Names
- English: Botrytis rot of leek; mycelial: onion neck rot; neck rot of onion; seedling damping-off of onion
- BOTTPO (Botryotinia porri)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Fungi
- Phylum: Ascomycota
- Subphylum: Pezizomycotina
- Class: Leotiomycetes
- Subclass: Leotiomycetidae
- Order: Helotiales
- Family: Sclerotiniaceae
- Genus: Botryotinia
- Species: Botryotinia porri
Notes on Taxonomy and NomenclatureTop of page
There has been a certain confusion in the literature about the species of Botryotinia and Botrytis on Allium (Lacy and Lorbeer, 1995). Moore (1959) cites Cronshey (1947) as considering that the onion pathogen Botrytis byssoidea is the anamorph of Botryotinia porri. On this basis, Botrytis porri would be a synonym of B. byssoidea. Smith et al. (1988) have followed this interpretation. However, most authors do not refer to any teleomorph of B. byssoidea, which is treated as though it were mitosporic. In fact, the teleomorph of B. byssoidea has been described in Japan as Botryotinia allii (Yamamoto et al., 1956). This is accepted by Jarvis (1980) and Farr et al. (1989). In particular, Hennebert (1973) clearly separates Botrytis porri from Botrytis byssoidea. The current authoritative view is thus that there are two distinct species, Botryotinia allii (with anamorph Botrytis byssoidea) and Botryotinia porri (with anamorph Botrytis porri), besides the third, Botryotinia squamosa (with anamorph Botrytis squamosa). Lacy and Lorbeer (1995) have suggested further that B. byssoidea may be conspecific with Botrytis allii (which has no known teleomorph). The situation needs further clarification. In any case, the polyphagous Botryotinia fuckeliana (anamorph Botrytis cinerea) is also found on Allium. Cases of 'Botrytis' on Allium may often be inadequately identified.
DescriptionTop of page A recent description has been provided by Crowe et al. (1995). The conidia resemble those of other species of Botrytis, appearing smoky brown in the mass. They are 7.5-19.5 x 6.0-13.0 µm, smooth, ellipsoid to spherical. In his comparative study of species of Botrytis on Allium, Presly (1985) found that B. porri isolates had conidia on average 15.7 x 9.6 µm, larger than those of B. byssoidea (13.0 x 7.5 µm) but smaller than those of B. squamosa (21.8 x 16.7 µm). The sclerotia are distinctively convoluted or cerebriform, and large (up to 2 cm), compared with those of B. squamosa. They germinate to give rise either to conidia or to apothecia. Up to 12 apothecia may form per sclerotium, each from a few mm to 4-5 cm long, and a disc of 5-8 mm diameter. Asci are 190-225 µm long, and ascospores 14.0-26.5 x 7.0-12.5 µm.
According to Presly (1985), B. porri does not abundantly produce conidia in culture (unlike B. allii). Like B. byssoidea, its mycelium is white and fluffy but it readily produces sclerotia, unlike B. byssoidea. B. squamosa produces smaller sclerotia on white ropy mycelium.
DistributionTop of page
The available information on the geographical distribution of B. porri appears incomplete. It has been recorded in several European countries on leeks, and in others on garlic but it seems likely that the fungus occurs more widely in Europe in leek and garlic-producing countries. Similarly, it seems likely that the species occurs more widely in North America than published records indicate. Apart from New Zealand, there are no specific records from other parts of the world, though the confusion with Botryotinia allii (see Notes on Taxonomy and Nomenclature) may have led to some misattribution of records. In many countries, cases of B. porri may readily have been misidentified as other species of Botrytis.
Specimens of B. porri held at CABI Bioscience (Egham, UK) are also cited in the distribution table (IMI Herbarium, undated).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|China||Present||Zhang et al., 2009|
|-Hubei||Present||Zhang et al., 2009|
|Iran||Present||Mirzaei et al., 2008|
|Canada||Restricted distribution||Asiedu et al., 1986|
|-Quebec||Present||Asiedu et al., 1986|
|USA||Restricted distribution||Somerville et al., 1984; Crowe et al., 1995|
|-California||Present||Somerville et al., 1984|
|-Nevada||Present||Somerville et al., 1984|
|-Oregon||Present||Somerville et al., 1984|
|-Washington||Present||Toit et al., 2002|
|Chile||Restricted distribution||IPPC, 2006|
|Venezuela||Present||Cedeño et al., 2003|
|Germany||Present||Bottcher and Pohle, 1991|
|Norway||Widespread||****||Roed, 1952; Hoftun, 1978|
|UK||Widespread||****||IMI Herbarium, undated; Cronshey, 1947; Cook, 1976|
|Australia||Present||Present based on regional distribution.|
|-New South Wales||Present||IMI Herbarium, undated|
|New Zealand||Present||IMI Herbarium, undated; Crowe et al., 1995|
Risk of IntroductionTop of page B. porri has not been reported from many areas of the world where species of Allium are cultivated. This suggests that there is a possibility of spread to new areas. However, the disease is favoured by cool temperate conditions, and is thus unlikely to establish in many of the areas where it is currently unknown. CPPC has listed it as a quarantine pest, but it does not seem very likely that B. porri would establish under tropical American conditions. Since the disease is only of moderate importance, and other species of Botrytis occur on Allium in many areas, it does not seem that the exclusion of B. porri has a very high priority.
Hosts/Species AffectedTop of page B. porri has only been recorded on leek and garlic in the field, but Presly (1985) was able to infect onions in the laboratory.
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page Post-harvest, Vegetative growing stage
SymptomsTop of page B. porri causes a neck rot of leek and garlic, which may cause the whole aboveground parts of the plant to die. Typical Botrytis conidia form on the neck of the bulbs, followed by sclerotia. In garlic, the rot may spread to the whole of the bulb during the growing season, with abundant production of sclerotia. In leek, plants are decayed in store.
List of Symptoms/SignsTop of page
|Vegetative organs / dry rot|
|Vegetative organs / internal rotting or discoloration|
|Vegetative organs / mould growth|
Biology and EcologyTop of page The life cycle of B. porri follows the typical pattern of the group. Survival is mainly as sclerotia in the soil. The fungus may possibly also survive in host debris. Formation of apothecia is a normal stage in the life cycle, but sclerotia can also give rise to conidia directly. The relative importance of ascospores and conidia in primary infection is not known. B. porri is favoured by cool moist conditions, which allow the dispersal of conidia in the early part of the growing season and thus the possibility of epidemic spread. The disease does not progress when conditions become warm and dry. Irrigation also favours infection.
Post-harvest damage arises from the spread of lesions formed in the field. In stored leeks, the fungus does not spread at storage temperatures of -1 to 0°C, but lesions expand at 5°C or above.
Means of Movement and DispersalTop of page Natural dispersal (non-biotic)
The fungus spreads by wind or rain dispersal of ascospores and conidia.
Crowe et al. (1995) mention that there are unconfirmed reports that B. porri may be seed-borne. Since B. porri does not apparently infect the above-ground parts of the plant, and is not known to produce the kind of latent infection which characterizes the seed-borne B. allii, such seed-borne transmission seems implausible.
Movement in trade
B. porri may be spread by planting material (bulbs of garlic, possibly young seedlings of leek). Internationally, it could also be introduced into new areas with garlic bulbs or leeks for consumption, although it is relatively unlikely that diseased material should enter international trade because of its obvious poor quality.
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bulbs/Tubers/Corms/Rhizomes||spores||Yes||Yes||Pest or symptoms usually visible to the naked eye|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|Growing medium accompanying plants|
|Stems (above ground)/Shoots/Trunks/Branches|
|True seeds (inc. grain)|
ImpactTop of page The disease is relatively little reported or studied in the countries where it occurs, which shows that it is in general only of moderate importance. Garlic is mostly grown in areas with a warm dry summer period, which limits the potential impact of B. porri. If cooler and moister conditions do occur, however, B. porri can cause considerable damage to garlic. On leek, the disease is mainly of concern post-harvest rather than in the field.
Detection and InspectionTop of page Stored garlic or leek should be examined for the presence of the characteristic sclerotia.
Similarities to Other Species/ConditionsTop of page B. porri resembles, and may be confused with, other species of Botryotinia/Botrytis on Allium. In practice, it is distinguished as the species occurring on leek or garlic. However, B. allii also occurs on garlic, and B. cinerea may occur on any of the species concerned.
Prevention and ControlTop of page Good hygiene will prevent the persistence of sclerotia or infected crop debris in the soil. Agricultural practices that would create cool moist conditions in the upper layers of the soil should be avoided, in particular in relation to irrigation. No particular chemical control is recommended. In store, leeks should be kept at a sufficiently low temperature. Alternatively, increasing the carbon dioxide content of the storage atmosphere, and decreasing the oxygen content, will prevent development of the fungus (Hoftun, 1978).
ReferencesTop of page
Cedeño L, Carrero C, Quintero K, Segovia P, 2003. Botrytis porri, causal agent of neck rot of garlic in Mérida, Venezuela. (Botrytis porri, Causante de pudrición en el cuello del ajo en Mérida, Venezuela.) Interciencia, 28(5):273-275.
Cronshey JFH, 1947. Sclerotinia porri on Allium spp. in England. Nature (London), 160:798.
Crowe F, Mohan SK, Schwartz HF, 1995. Botrytis rot of garlic. In: Schwartz HF, Mohan SK, eds. Compendium of Onion and Garlic Diseases. St Paul, USA: American Phytopathological Society, 19-20.
IMI Herbarium, undated. Herbarium specimen. International Mycological Institute (now CABI Bioscience) Herbarium. Egham, UK: CABI Bioscience.
IPPC, 2006. IPP Report No. CL-2/1. Rome, Italy: FAO.
Jarvis WR, 1980. Taxonomy. In: Coley-Smith JR, Verhoeff K, Jarvis WR, eds. The Biology of Botrytis. London, UK: Academic Press, 1-18.
Lacy ML, Lorbeer JW, 1995. Botrytis neck rot. In: Schwartz HF, Mohan SK, eds. Compendium of Onion and Garlic Diseases. St Paul, USA: American Phytopathological Society, 18-19.
Mirzaei S, Goltapeh EM, Shams-Bakhsh M, Safaie N, 2008. Identification of Botrytis spp. on plants grown in Iran. Journal of Phytopathology, 156(1):21-28. http://www.blackwell-synergy.com/doi/abs/10.1111/j.1439-0434.2007.01317.x
Moore WC, 1959. British parasitic fungi. Cambridge, UK: Cambridge University Press, 430 pp.
Roed H, 1952. Botryotinia porri on Allium porrum in Norway. Acta Agriculturae Scandinavica, 2;232-241.
Somerville PA, Hall DH, Greathead AS, 1984. Dry rot of garlic caused by Botrytis porri. Phytopathology, 74:829.
Yamamoto, W. , Oyasu, N. , Iwasaki, A. , 1956. Studies on the leaf blight disease of Allram spp. caused by Botrytis and Botryotinia fungi., L. Sci. Rep. Hyogo Univ. Agric. Ser. Agric. Biol., 2(2):17-22
Distribution MapsTop of page
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