Calonectria pseudonaviculata (Buxus blight)
Index
- Pictures
- Identity
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Description
- Distribution
- Distribution Table
- Introductions
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- Symptoms
- List of Symptoms/Signs
- Biology and Ecology
- Climate
- Means of Movement and Dispersal
- Pathway Causes
- Pathway Vectors
- Plant Trade
- Impact Summary
- Economic Impact
- Risk and Impact Factors
- Diagnosis
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Gaps in Knowledge/Research Needs
- References
- Contributors
- Distribution Maps
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Top of pagePreferred Scientific Name
- Calonectria pseudonaviculata (Crous, J.Z. Groenew. & C.F. Hill) L. Lombard, M.J. Wingf. & Crous, 2010
Preferred Common Name
- Buxus blight
Other Scientific Names
- Cylindrocladium buxicola Henricot 2002
- Cylindrocladium pseudonaviculatum Crous, J.Z. Groenew. & C.F. Hill, 2002
International Common Names
- English: box blight; boxwood blight; boxwood leaf drop; leaf and twig blight of box
EPPO code
- CYLDBU (Cylindrocladium buxicola)
Summary of Invasiveness
Top of pageC. pseudonaviculata is an asexual species in a genus of common ascomycete plant pathogens. It was identified relatively recently in the UK, as an introduced species causing a devastating shoot blight of boxwood [Buxus spp.] plants that are commonly used in gardens and landscaping. The full extent of its host range is not known, but Buxus spp. from different continents were found to be susceptible (Henricot et al., 2008). It was placed on the EPPO Alert list in 2004, as it appeared to be spreading to the mainland (EPPO, 2009a), and removed from the list in 2008. This pathogen has been reported from additional European countries in recent years, and may have been transported in asymptomatic infected plants or propagating materials. It survives well in plant debris and probably also in soil.
Taxonomic Tree
Top of page- Domain: Eukaryota
- Kingdom: Fungi
- Phylum: Ascomycota
- Subphylum: Pezizomycotina
- Class: Sordariomycetes
- Subclass: Hypocreomycetidae
- Order: Hypocreales
- Family: Nectriaceae
- Genus: Calonectria
- Species: Calonectria pseudonaviculata
Notes on Taxonomy and Nomenclature
Top of pageCylindrocladium pseudonaviculatum was first described by Crous et al. (2002). The description of Cylindrocladium buxicola followed a few months later in the same year (Henricot and Culham, 2002), which later proved to be synonymous with Calonectria pseudonaviculata (Lombard et al., 2010). The taxon was determined to be a new species both by examination of morphology and comparison of sequences of several regions of nuclear DNA. No sexual morph could be obtained by mating of single spore cultures on carnation leaf agar (CLA), and the similarity of amplified fragment length polymorphism (AFLP) profiles of the different isolates indicated that all were probably descended from one clone.
Sexual morphs of Cylindrocladium species are members of Calonectria, in the Hypocreales (Rossman, 1993; Crous, 2002). The current scientific name for this species is Calonectria pseudonaviculata (Crous, J.Z. Groenew. & C.F. Hill) L. Lombard, M.J. Wingf. & Crous.
Description
Top of pageConidiophores comprised of a stipe, sterile stipe extension with a terminal vesicle, and penicillate arranged branches bearing phialides. Stipe septate, hyaline, 95-155 µm, the stipe extension terminating in a broadly ellipsoid vesicle, vesicle apex pointed to papillate, 6.5-11.0 µm diameter, the widest part above the middle. Primary branches 0-1-septate, (5-)15-41(-66) x 3-5 µm, secondary branches aseptate, (11-)13-25(-35) x 3-5 µm, tertiary branches rare. Terminal branches bearing two to five phialides. Phialides reniform, hyaline, aseptate, (10-)13-18(-21) x 2.5-5.0 µm. Conidia cylindrical, straight, hyaline, 1-septate, the ends rounded, 42-68 x 4-6 µm, in slimy clusters. Chlamydospores on carnation [Dianthus caryophyllus] leaves dark-brown, thick-walled, forming microsclerotia. Reverse of colony on malt extract agar (MEA) fuscous black at centre fading through sienna outwards. Mycelium at margin white. For additional details, see Henricot and Culham (2002).
Distribution
Top of pageThe new disease of boxwood (Buxus spp.) was first observed in 1994 in the UK, and a more severe outbreak occurred in 1997 (Henricot and Culham, 2002). Although the pathogen is considered to have been recently introduced (Brasier, 2008), it was already widespread in the UK by 2000 (Henricot et al., 2000). An isolate from New Zealand was determined by Henricot and Culham (2002) to be of the same species and closely related to the strains in the UK. Reports of C. pseudonaviculata have since come from Belgium, Ireland, Germany and the Netherlands (CABI/EPPO, 2012; Henricot et al., 2008), Italy (Saracchi et al., 2008; EPPO, 2013), Austria (EPPO, 2013) and Spain (Pintos Varela et al., 2009) suggesting that it spread from the UK to mainland Europe.
Distribution Table
Top of pageThe 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.
Last updated: 12 May 2022Continent/Country/Region | Distribution | Last Reported | Origin | First Reported | Invasive | Reference | Notes |
---|---|---|---|---|---|---|---|
Asia |
|||||||
Georgia | Present | ||||||
Iran | Present | ||||||
Turkey | Present | ||||||
Europe |
|||||||
Austria | Present, Few occurrences | Introduced | |||||
Belgium | Present, Widespread | Introduced | Invasive | ||||
Czechia | Present, Localized | ||||||
Denmark | Present | ||||||
France | Present | Introduced | Invasive | ||||
Germany | Present, Widespread | Introduced | Invasive | First seen 2004 | |||
Ireland | Present | Introduced | Invasive | ||||
Italy | Present, Localized | Introduced | 2007 | Invasive | |||
Netherlands | Present | Introduced | Invasive | ||||
Norway | Present, Localized | ||||||
Russia | Present | ||||||
-Southern Russia | Present | ||||||
Slovenia | Present | ||||||
Spain | Present | Introduced | Invasive | ||||
Sweden | Present, Few occurrences | ||||||
Switzerland | Present | Introduced | Invasive | ||||
United Kingdom | Present, Widespread | Introduced | Invasive | ||||
-England | Present | ||||||
-Scotland | Present | ||||||
North America |
|||||||
Canada | Present, Localized | ||||||
-British Columbia | Present, Localized | ||||||
-Ontario | Present, Few occurrences | ||||||
-Quebec | Present, Few occurrences | ||||||
United States | Present, Localized | ||||||
-Alabama | Present | ||||||
-Arkansas | Present | ||||||
-California | Present, Localized | ||||||
-Connecticut | Present | ||||||
-Delaware | Present | ||||||
-Florida | Present | ||||||
-Georgia | Present | ||||||
-Illinois | Present | ||||||
-Indiana | Present | ||||||
-Kansas | Present | ||||||
-Kentucky | Present | ||||||
-Maryland | Present | ||||||
-Massachusetts | Present | ||||||
-Michigan | Present | ||||||
-Missouri | Present | ||||||
-New Hampshire | Present | ||||||
-New Jersey | Present | ||||||
-New York | Present | ||||||
-North Carolina | Present | ||||||
-North Dakota | Present | ||||||
-Ohio | Present | ||||||
-Oregon | Present | ||||||
-Pennsylvania | Present | ||||||
-Rhode Island | Present | ||||||
-South Carolina | Present | ||||||
-South Dakota | Present | ||||||
-Tennessee | Present | ||||||
-Virginia | Present | ||||||
-Washington | Present | ||||||
-West Virginia | Present | ||||||
-Wisconsin | Present | ||||||
Oceania |
|||||||
New Zealand | Present | Introduced | Invasive |
Introductions
Top of pageIntroduced to | Introduced from | Year | Reason | Introduced by | Established in wild through | References | Notes | |
---|---|---|---|---|---|---|---|---|
Natural reproduction | Continuous restocking | |||||||
Italy | Horticulture (pathway cause) | EPPO (2009); EPPO (2009a); Saracchi et al. (2008) | more than one accidental introduction(?) - observed at 2 locations |
Risk of Introduction
Top of pageThe origin of C. pseudonaviculata is not known; it is considered to be an introduced alien species in the UK, where it was first identified (Brasier, 2008). Transmission of the pathogen on asymptomatic Buxus plants, as suggested by Henricot and Culham (2002), may be responsible for its rapid spread in the UK and to various countries of Western Europe. It is also possible, given the wide host ranges of some Calonectria spp. and the possibility of their misidentification (see Henricot and Culham, 2002; Lombard et al. 2010), that an introduction on some other host went unchallenged because the fungus resembled a widespread species.
Habitat List
Top of pageCategory | Sub-Category | Habitat | Presence | Status |
---|---|---|---|---|
Terrestrial | Managed | Cultivated / agricultural land | Present, no further details | Harmful (pest or invasive) |
Hosts/Species Affected
Top of pageThe disease has only been found in some cultivars of three species out of the 91 in the genus Buxus worldwide: B. sempervirens,B. microphylla and B. sinica var. insularis (Henricot et al., 2008). When detached stems of other species, including plants native to four continents, were tested beside these, Henricot et al. (2008) found no immunity to the fungus. Differences between the species were not consistent in tests with different isolates of the pathogen. The lowest level of disease was observed in B. balearica, B. riparis and a Sarcococca sp.Sarcococca is a genus in the Buxaceae that includes some species imported for use as ground cover; Pachysandra species, also members of the family often used for ground cover, were not tested (Henricot et al., 2008).
Host Plants and Other Plants Affected
Top of pagePlant name | Family | Context | References |
---|---|---|---|
Buxus (box) | Buxaceae | Other | |
Buxus microphylla (little-leaf box) | Buxaceae | Main | |
Buxus microphylla var. japonica | Buxaceae | Main | |
Buxus sempervirens (common boxwood) | Buxaceae | Main | Gorgiladze et al. (2011); Blomquist et al. (2018); Cech et al. (2010); Crepel and Inghelbrecht (2003); Crous et al. (2002); Elmhirst et al. (2013); Gehesquière et al. (2016); Henricot and Culham (2002); Ivors et al. (2012); Lehtıjärvı et al. (2014); Pintos et al. (2009); Safránková et al. (2012); Saracchi et al. (2008); Yang and Hong (2018); Gauthier et al. (2016); Iriarte et al. (2016); Matsiakh et al. (2018) |
Buxus sinica (chinese box) | Buxaceae | Main | |
Buxus sinica var. insularis (Korean boxwood) | Buxaceae | Main | |
Pachysandra axillaris | Unknown | ||
Pachysandra procumbens | Buxaceae | Other | |
Pachysandra terminalis (Japanese spurge) | Buxaceae | Other | LaMondia et al. (2012); Kong et al. (2017) |
Sarcococca | Other | ||
Sarcococca hookeriana | Buxaceae | Unknown | |
Sarcococca hookeriana var. digyna | Buxaceae | Other | Kong et al. (2017) |
Symptoms
Top of pageThe fungus causes dark-brown leaf spots, which may coalesce to cover whole leaves, black streaks on stems that appear to progress from the bottom of the plant to the top, and severe defoliation and dieback (Henricot et al., 2000, 2008; Henricot and Culham, 2002).
List of Symptoms/Signs
Top of pageSign | Life Stages | Type |
---|---|---|
Growing point / dieback | ||
Leaves / abnormal leaf fall | ||
Leaves / necrotic areas | ||
Stems / dieback | ||
Stems / discoloration of bark |
Biology and Ecology
Top of pageLife Cycle
Conidia dispersed in water germinated on Buxus leaves beginning 3 hours after inoculation. Germ tubes penetrated through stomata or directly through the cuticle without forming an appressorium. Conidiophores were produced on the leaf surface after 7 days in a moist chamber at 20°C (Henricot et al., 2008). High humidity is required for infection of inoculated plants (Henricot et al., 2000).
In culture on PCA (potato-carrot agar), optimum growth occurs at 25°C. Growth is very slow at 27.5°C, and no growth was observed at 30°C. Incubation at 33°C for 7 days is lethal, and the low limit for growth is above 5°C (Henricot and Culham, 2002).
Mycelium of the fungus survived 5 years in decomposing leaves on or in soil in southern England, but microsclerotia were not seen (Henricot et al., 2008). Most Calonectria species are readily recovered from soil (Crous, 2002).
Reproductive Biology
No sexual reproductive structures have been observed in nature or in culture. The UK isolates examined by Henricot and Culham (2002), as well as one from New Zealand, exhibited little variation in AFLP patterns, thus appearing to be derived from one clone.
Climate
Top of pageClimate | Status | Description | Remark |
---|---|---|---|
Cf - Warm temperate climate, wet all year | Preferred | Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year |
Means of Movement and Dispersal
Top of pageNatural Dispersal
The 'slimy' conidia are easily splash-dispersed by water (Crous, 2002).
Vector Transmission
None is reported, but Crous (2002) hypothesizes a role for the stipe extension vesicle in attracting insects to the conidiophore.
Accidental Introduction
The fungus could be brought into gardens or nurseries on asymptomatic plants (Henricot et al., 2008).The means of introduction into the UK and mainland Europe could be the same, but is not known. In a nursery in Italy, potted plants that became infected had been without symptoms when imported from Belgium, where the pathogen was known to be present (Saracchi et al., 2008).
Pathway Causes
Top of pageCause | Notes | Long Distance | Local | References |
---|---|---|---|---|
Horticulture | Infected nursery stock/propagating material | Yes | Yes | Henricot et al. (2008); Saracchi et al. (2008) |
Pathway Vectors
Top of pageVector | Notes | Long Distance | Local | References |
---|---|---|---|---|
Plants or parts of plants | Infected plants | Yes | Yes | Henricot and Culham (2002); Saracchi et al. (2008) |
Water | Water-splash | Yes | Crous (2002) |
Plant Trade
Top of pagePlant parts liable to carry the pest in trade/transport | Pest stages | Borne internally | Borne externally | Visibility of pest or symptoms |
---|---|---|---|---|
Bark | fungi/hyphae | Yes | Yes | Pest or symptoms not visible to the naked eye but usually visible under light microscope |
Leaves | fungi/hyphae; fungi/spores | Yes | Yes | Pest or symptoms not visible to the naked eye but usually visible under light microscope |
Stems (above ground)/Shoots/Trunks/Branches | fungi/hyphae; fungi/spores | Yes | Yes | Pest or symptoms not visible to the naked eye but usually visible under light microscope |
Plant parts not known to carry the pest in trade/transport |
---|
Bulbs/Tubers/Corms/Rhizomes |
Flowers/Inflorescences/Cones/Calyx |
Fruits (inc. pods) |
Seedlings/Micropropagated plants |
True seeds (inc. grain) |
Wood |
Economic Impact
Top of pageThe disease is described as 'devastating' to boxwood (Buxus spp.) plants, which are widely used as landscape ornamentals (Henricot et al., 2008). Infected imported potted plants in an Italian nursery were destroyed due to the severity of disease (Saracchi et al., 2008).
Risk and Impact Factors
Top of page- Highly mobile locally
- Long lived
- Fast growing
- Has high reproductive potential
- Reproduces asexually
- Host damage
- Negatively impacts agriculture
- Negatively impacts livelihoods
- Reduced amenity values
- Pathogenic
- Highly likely to be transported internationally accidentally
- Difficult to identify/detect as a commodity contaminant
Diagnosis
Top of pageIsolates may be grown on PCA (potato-carrot agar), but culture on carnation leaf agar at 25°C under near-UV light is required for production of conidiophores with diagnostic morphology (Crous and Wingfield, 1994).
Comparison of sequences of the ITS region is insufficient to distinguish all the known species of Calonectria (Crous et al., 1999; Henricot and Culham, 2002). Instead, sequences of the 5' end of the beta-tubulin gene, the HMG box of the MAT2 gene, and partial sequences of the histone H3 gene have been used (Crous et al., 1999, 2002, 2006; Henricot and Culham, 2002). Most of these sequences, including at least eight for C. pseudonaviculata, are available in the GenBank database for comparison (Lombard et al., 2010).
Detection and Inspection
Top of pageThis pathogen causes dark leaf spots, dark streaks on the stems, and eventual defoliation of Buxus species. Conidiophores bearing clusters of distinctive large cylindrical conidia and a vesicle-tipped sterile stipe extension are produced on shoots incubated in a moist chamber at 20°C (Henricot and Culham, 2002).
Similarities to Other Species/Conditions
Top of pageCalonectria pseudonaviculata is distinguished from C. morganii and C. pyrochroa by the shape of the terminal vesicle and the size and septation of its conidia (Henricot and Culham, 2002). The vesicles of C. morganii are not pointed, and those of C. pyrochroa are spathulate to clavate. In addition, C. morganii and C. pyrochroa grow at 30°C and above (Crous and Wingfield, 1994) whereas 30°C is the maximum growth temperature for C. pseudonaviculata (Henricot and Culham, 2002). Other species, C. pauciramosa and C. mexicana, that have somewhat similar vesicles, are also warm-temperature species, with growth maxima of 30°C or above (Henricot and Culham, 2002).
Prevention and Control
Top of pageDue to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Prevention
SPS Measures
The likelihood that the pathogen is transported across borders in asymptomatic plants (Henricot et al., 2008; Saracchi et al., 2008) would require restriction of trade of boxwood (Buxus spp.) plants and vegetative propagating material, such as cuttings, including either quarantine or certification procedures to prevent further spread of the fungus. If there is a possibility that it was, or can be, introduced on other hosts upon which it has been misidentified, stricter attention to identifications of Calonectria pathogens, with the aid of molecular methods, may be necessary.
Control
Cultural Control and Sanitary Measures
C. pseudonviculata can persist for years in plant debris on or in the ground, therefore removing infected twigs, fallen leaves and the topsoil under affected plants are reasonable efforts to reduce inoculum (Henricot et al., 2008). Batdorf (2004) asserts that regular fall pruning to thin the branches of Buxus sempervirens "Suffruticosa" will control fungal foliage diseases such as Cylindrocladium blight.
Chemical Control
Henricot et al. (2008) tested a number of fungicide products available in the UK. Those most effective at inhibiting mycelial growth of C. pseudonaviculata in vitro were carbendazim, prochloraz, kresoxim-methyl, penconazole, the combination of epiconazole and pyraclostrobin, and the combination of epiconazole+kresoxim-methyl+pyraclostrobin. Those most effective at inhibiting conidial germination in vitro were azoxystrobin, chlorothalonil, kresoxim-methyl, mancozeb, boscalid+pyraclostrobin, epiconazole+pyraclostrobin, and the combination of epiconazole+kresoxim-methyl+pyraclostrobin. Carbendazim, myclobutanil, penconazole and prochloraz had little or no effect on germination.
Chlorothalonil, which was the most inhibiting to spore germination in vitro, has also been reported as effective in the field (Henricot et al., 2008).
Host Resistance
Differences in isolate-species interactions observed by Henricot et al. (2008) suggest a potential for use of varieties and species in landscaping of areas where the pathogen is known to occur. Unfortunately, the growth habit that contributes to the ornamental desirability of the susceptible species and varieties may favour the development of disease (Henricot et al., 2008).
Gaps in Knowledge/Research Needs
Top of pageMany Calonectria species infect roots (Crous, 2002); whether C. pseudonaviculata can infect those of Buxus or other plants, should be investigated. The possible role of chlamydospores and microsclerotia in survival in plant tissues and in soil should be examined further. Efforts to discover the origin of the fungus and to explore the possibility of insect vectors for Calonectria species could help to prevent further introductions.
References
Top of pageEPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
Lombard L; Crous PW; Wingfield BD; Wingfield MJ, 2010. Phylogeny and systematics of the genus Calonectria. Studies in Mycology, 66:31-69.
NAPPO, 2011. Phytosanitary Alert System: Detection of boxwood blight, Cylindrocladium pseudonaviculatum, in Connecticut, North Carolina, and Virginia. Phytosanitary Alert System: Detection of boxwood blight, Cylindrocladium pseudonaviculatum, in Connecticut, North Carolina, and Virginia. NAPPO. http://www.pestalert.org/oprDetail.cfm?oprID=508
Distribution References
CABI, Undated. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI
NAPPO, 2011. Phytosanitary Alert System: Detection of boxwood blight, Cylindrocladium pseudonaviculatum, in Connecticut, North Carolina, and Virginia., NAPPO. http://www.pestalert.org/oprDetail.cfm?oprID=508
Contributors
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