Invasive Species Compendium

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Datasheet

Gibberella circinata
(pitch canker)

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Datasheet

Gibberella circinata (pitch canker)

Summary

  • Last modified
  • 14 July 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Natural Enemy
  • Preferred Scientific Name
  • Gibberella circinata
  • Preferred Common Name
  • pitch canker
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Fungi
  •     Phylum: Ascomycota
  •       Subphylum: Pezizomycotina
  •         Class: Sordariomycetes
  • Summary of Invasiveness
  • G. circinata gained its reputation as an invasive pest following its discovery in California, USA, in 1986. Although the disease was well established by that time, it is clear the infestation expanded rapidly over the next 10 years. For example, surv...

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Pictures

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PictureTitleCaptionCopyright
Uniformly yellow foliage on Pinus radiata resulting from an infection that has girdled the stem of the tree at the soil line.
TitleSymptoms
CaptionUniformly yellow foliage on Pinus radiata resulting from an infection that has girdled the stem of the tree at the soil line.
CopyrightTom Gordon
Uniformly yellow foliage on Pinus radiata resulting from an infection that has girdled the stem of the tree at the soil line.
SymptomsUniformly yellow foliage on Pinus radiata resulting from an infection that has girdled the stem of the tree at the soil line.Tom Gordon
Accumulated resin at the site of a pitch infection on Pinus radiata.
TitleSymptoms
CaptionAccumulated resin at the site of a pitch infection on Pinus radiata.
CopyrightTom Gordon
Accumulated resin at the site of a pitch infection on Pinus radiata.
SymptomsAccumulated resin at the site of a pitch infection on Pinus radiata.Tom Gordon
A naked branch tip and dead needles resulting from a girdling lesion on Pinus radiata.
TitleSymptoms
CaptionA naked branch tip and dead needles resulting from a girdling lesion on Pinus radiata.
CopyrightTom Gordon
A naked branch tip and dead needles resulting from a girdling lesion on Pinus radiata.
SymptomsA naked branch tip and dead needles resulting from a girdling lesion on Pinus radiata.Tom Gordon
Wilting of a succulent branch tip resulting from a girdling lesion on Pinus radiata.
TitleSymptoms
CaptionWilting of a succulent branch tip resulting from a girdling lesion on Pinus radiata.
CopyrightTom Gordon
Wilting of a succulent branch tip resulting from a girdling lesion on Pinus radiata.
SymptomsWilting of a succulent branch tip resulting from a girdling lesion on Pinus radiata.Tom Gordon
Pinus radiata with multiple dead branch tips, each resulting from an independent infection by G. circinata.
TitleSymptoms
CaptionPinus radiata with multiple dead branch tips, each resulting from an independent infection by G. circinata.
CopyrightTom Gordon
Pinus radiata with multiple dead branch tips, each resulting from an independent infection by G. circinata.
SymptomsPinus radiata with multiple dead branch tips, each resulting from an independent infection by G. circinata.Tom Gordon
Pinus radiata with a complete loss of canopy due to multiple infections of branches and on the main stem.
TitleSymptoms
CaptionPinus radiata with a complete loss of canopy due to multiple infections of branches and on the main stem.
CopyrightTom Gordon
Pinus radiata with a complete loss of canopy due to multiple infections of branches and on the main stem.
SymptomsPinus radiata with a complete loss of canopy due to multiple infections of branches and on the main stem.Tom Gordon
Streaming resin on Pinus radiata resulting from infections on the main stem of the tree.
TitleSymptoms
CaptionStreaming resin on Pinus radiata resulting from infections on the main stem of the tree.
CopyrightTom Gordon
Streaming resin on Pinus radiata resulting from infections on the main stem of the tree.
SymptomsStreaming resin on Pinus radiata resulting from infections on the main stem of the tree.Tom Gordon

Identity

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Preferred Scientific Name

  • Gibberella circinata Nirenberg & O'Donnell 1998

Preferred Common Name

  • pitch canker

Other Scientific Names

  • Fusarium circinatum Nirenberg & O'Donnell 1998
  • Fusarium lateritium f.sp. pini Snyder et al.
  • Fusarium moniliforme var. subglutinans Wollenw. & Reinking
  • Fusarium subglutinans (Wollenw. & Reinking) P.E. Nelson et al.
  • Fusarium subglutinans f.sp. pini J.C. Correll et al.
  • Gibberella baccata f.sp. pini
  • Gibberella fujikuroi var. subglutinans E.T. Edwards
  • Gibberella subglutinans (E.T. Edwards) P.E. Nelson et al.

International Common Names

  • English: canker: pitch pine

EPPO code

  • GIBBCI (Gibberella circinata)

Summary of Invasiveness

Top of page G. circinata gained its reputation as an invasive pest following its discovery in California, USA, in 1986. Although the disease was well established by that time, it is clear the infestation expanded rapidly over the next 10 years. For example, surveys revealed no evidence of pitch canker in the native forest on the Monterey Peninsula prior to 1992. Thereafter, the incidence and severity of the disease increased dramatically. The rapid development of pitch canker in coastal California can be attributed to the widespread availability of a highly susceptible host (Pinus radiata), a conducive climate and an abundance of pine-associated insects capable of serving as vectors and wounding agents. Since the discovery of pitch canker in California, the disease has also been found in Japan where it appears to be a recent introduction (Wikler and Gordon, 2000). G. circinata has also become established as a pathogen in pine seedling nurseries in South Africa (Viljoen et al., 1994), Spain (Dwinell, 1999b) and Chile (Wingfield et al., 2002). The ability of the pathogen to be moved as infested seed, to survive in soil and to establish latent infections on seedlings greatly facilitate its potential for dispersal and establishment wherever susceptible pines are grown.

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Fungi
  •         Phylum: Ascomycota
  •             Subphylum: Pezizomycotina
  •                 Class: Sordariomycetes
  •                     Subclass: Hypocreomycetidae
  •                         Order: Hypocreales
  •                             Family: Nectriaceae
  •                                 Genus: Gibberella
  •                                     Species: Gibberella circinata

Notes on Taxonomy and Nomenclature

Top of page The fungus that causes pitch canker was originally thought to be Fusarium lateritium (Snyder et al., 1949) but was later recognized as Fusarium moniliforme var. subglutinans (Kuhlman et al., 1978). Thus, the pitch canker pathogen was assigned to an anamorphic taxon that was already known to include a number of strains associated with different hosts, some of which had a perfect state: Gibberella fujikuroi var. subglutinans. This variety was eventually accorded specific status (= F. subglutinans and G. subglutinans) by Nelson et al. (1983). Distinct 'mating populations' (i.e. biological species) were recognized within the G. fujikuroi complex, by Hsieh et al. (1977); these were designated by letters (A-C, initially but eventually also including D-H), but there was not a 1:1 correspondence with anamorphic species. Thus, the F. subglutinans morphotype was associated with mating populations B and E (Leslie, 1995). Laboratory crosses indicated fertility of the pitch canker pathotype with testers of mating population E. However, this result was misleading and may have been due to selfing, which is now known to occur in the 'E' testers. Given the lack of fertility with other mating populations, distinctive genetic characteristics, and an apparently unique host range, the pitch canker pathotype was designated as F. subglutinans f.sp. pini (Correll et al., 1991). Fertility under laboratory conditions was finally demonstrated, and the pitch canker pathogen was confirmed to constitute a distinct biological species (Britz et al., 1999b), which was given the name G. circinata (=G. fujikuroi mating population H) (Nirenberg and O'Donnell, 1998).

Description

Top of page The name Gibberella circinata denotes the teleomorph (sexual) stage of the pitch canker pathogen. Its distinctive feature is the perithecium, which contains meiotically derived spores (ascospores). Ascomata (perithecia) have not been observed in nature, but they are readily produced on culture media whereon they are dark purple to black, and ovoid to obpyriform. Nirenberg and O'Donnell (1998) gave the dimensions of the ascoma as 325 µm high and 230 µm wide. Britz et al. (2002), however, found ascoma to be larger: 332-396-453 µm high and 288-337-358 µm wide. Ascoma contain cylindrical-shaped asci: 88-100 x 7.5-8.5 µm (Nirenberg and O'Donnell, 1998), which ooze from the ascoma at maturity. Each ascus nominally contains eight ascospores, which are typically 1-septate and ellipsoidal to fusiform. The teleomorph of G. circinata is similar in appearance to closely related species, which are more readily distinguished on the basis of the morphology of the anamorph.

The anamorphic form (Fusarium circinatum) is characterized by the production of macro- and microconidia, which are mitotically derived spores that serve to propagate the fungus under natural conditions. Both spore types are formed on natural substrata and on artificial growth media. Macroconidia are typically 3-septate, with walls that are slightly curved to nearly parallel throughout. The apical cell narrows to an inwardly (i.e. toward the ventral side) curved tip, and the basal cell is foot-shaped (i.e. it has a slight indentation or notch on the dorsal side). Nirenberg and O'Donnell (1998) report macroconidial dimensions as in the range 32-48 x 3.3-3.8 µm. The shape and size of the macroconidium in F. circinatum is similar to that in numerous other species (including many formerly grouped together in section Liseola) and thus is of limited diagnostic value. Microconidia are typically single-celled but may be septate, and are usually ovoid but can be more nearly oval or, less often, allantoid. Microconidia are borne in false heads on aerial polyphialides. In culture, the proliferation of microconidiophores, coupled with a slight twisting of the aerial mycelium on which they are borne, gives F. circinatum a distinctive colony morphology. Aerial mycelium is white, but may have slight purple or violet pigmentation. The underside of a culture may be colourless or show various colorations depending on the isolate, growth medium and culture conditions. Sectors, which form readily in some isolates, frequently differ in colour from the 'parent' colony, indicating that pigmentation is a highly mutable characteristic.

Distribution

Top of page In the USA, pitch canker occurs in nine states in the south-east and in coastal, but not inland, areas of California. There is a single report of pitch canker from the state of Indiana on nursery stock of P. strobus. Records for the states of Washington and Massachusetts which were published in the 1998 CABI/EPPO distribution map for G. circinata are incorrect; pitch canker has never been reported from these states (Ridley and Dick, 2000). Records of pitch canker from Italy (Motta, 1986) and Iraq (Khalisy et al., 1981) are questionable. These reports were based on isolation of Fusarium moniliforme var. subglutinans from seed (Italy) or nursery stock exhibiting damping-off (Iraq). Due to the ambiguous taxonomy of the pine pathogen over time (see Notes on Taxonomy and Nomenclature) and the fact that pathogenicity of these isolates to pines was not demonstrated, it is uncertain whether these were the pitch canker pathogen. The absence of any subsequent reports from these areas suggests they were not. No further observations on the occurrence of pitch canker in Haiti have been published since the original report by Hepting in 1953. In Mexico, the disease is known from at least 15 states. In Chile and South Africa the disease is now well established but is known only from nurseries. It is present in Japan but may be more important in Korea (J Kim, University of Seoul, Korea, personal communication).

Distribution Table

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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/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

IraqAbsent, unreliable recordEPPO, 2014
JapanPresent1990CABI/EPPO, 2012; EPPO, 2014
-KyushuPresentMuramoto et al., 1993; CABI/EPPO, 2012; EPPO, 2014
-Ryukyu ArchipelagoWidespreadMuramoto and Dwinell, 1990; Kobayashi and Kawabe, 1992; CABI/EPPO, 2012; EPPO, 2014
Korea, Republic ofRestricted distributionCABI/EPPO, 2012; EPPO, 2014; Han et al., 2015Western Korea in urban and forest plantations. Gongju, Taean, Gapyeong
PhilippinesAbsent, unreliable recordEPPO, 2014
TurkeyAbsent, confirmed by surveyEPPO, 2014

Africa

AlgeriaAbsent, confirmed by surveyEPPO, 2014
South AfricaRestricted distribution1990Britz et al., 1999a; Viljoen et al., 1994; CABI/EPPO, 2012; EPPO, 2014
TanzaniaAbsent, unreliable recordEPPO, 2014

North America

MexicoPresentGuerra-Santos, 1999; Britz et al., 2001; CABI/EPPO, 2012; EPPO, 2014
USARestricted distributionCABI/EPPO, 2012; EPPO, 2014
-AlabamaPresentHepting and Roth, 1953; Kelley, 1982; Barrows-Broaddus and Dwinell, 1984; CABI/EPPO, 2012; EPPO, 2014
-ArkansasPresentCABI/EPPO, 2012; EPPO, 2014
-CaliforniaPresent1986McCain et al., 1987; Correll et al., 1991; Storer et al., 1994; Gordon et al., 2001; CABI/EPPO, 2012; Swett and Gordon, 2012; EPPO, 2014
-FloridaPresentHepting and Roth, 1953; Dwinell and Phelps, 1977; Blakeslee and Oak, 1979; CABI/EPPO, 2012; EPPO, 2014
-GeorgiaPresentHepting and Roth, 1953; Dwinell, 1978; CABI/EPPO, 2012; EPPO, 2014
-IndianaPresentMcCay-Buis et al., 1994
-LouisianaPresentDwinell et al., 1985; CABI/EPPO, 2012; EPPO, 2014
-MassachusettsAbsent, unreliable recordCABI/EPPO, 2012; EPPO, 2014
-MississippiPresentHepting and Roth, 1953; Dwinell, 1978; CABI/EPPO, 2012; EPPO, 2014
-North CarolinaPresent1946Hepting and Roth, 1946; Dwinell, 1978; Kuhlman et al., 1982; Kuhlman and Cade, 1985; CABI/EPPO, 2012; EPPO, 2014
-South CarolinaPresentHepting and Roth, 1946; Kraus and Witcher, 1977; CABI/EPPO, 2012; EPPO, 2014
-TennesseePresentHepting and Roth, 1953; Dwinell, 1978; CABI/EPPO, 2012; EPPO, 2014
-TexasPresentDwinell et al., 1985; Barrows-Broaddus, 1987; CABI/EPPO, 2012; EPPO, 2014
-VirginiaPresentHepting and Roth, 1953; Dwinell, 1978; CABI/EPPO, 2012; EPPO, 2014
-WashingtonAbsent, unreliable recordCABI/EPPO, 2012; EPPO, 2014

Central America and Caribbean

HaitiPresentHepting and Roth, 1953; CABI/EPPO, 2012; EPPO, 2014
HondurasAbsent, unreliable recordEPPO, 2014

South America

ChileRestricted distributionWingfield et al., 2002; CABI/EPPO, 2012; EPPO, 2014
UruguayPresent, few occurrencesCABI/EPPO, 2012; EPPO, 2014

Europe

BelgiumAbsent, confirmed by surveyEPPO, 2014
CyprusAbsent, confirmed by surveyEPPO, 2014
DenmarkAbsent, confirmed by surveyEPPO, 2014
EstoniaAbsent, confirmed by surveyEPPO, 2014
FinlandAbsent, confirmed by surveyEPPO, 2014
FranceEradicatedCABI/EPPO, 2012; EPPO, 2014
GermanyAbsent, confirmed by surveyEPPO, 2014
HungaryAbsent, confirmed by surveyEPPO, 2014
ItalyAbsent, intercepted onlyCABI/EPPO, 2012; EPPO, 2014
LithuaniaAbsent, confirmed by surveyIPPC, 2016
MaltaAbsent, confirmed by surveyEPPO, 2014
NetherlandsAbsent, confirmed by surveyNPPO of the Netherlands, 2013; EPPO, 2014Based on long-term annual surveys, 185 survey observations in 2012.
NorwayAbsent, confirmed by surveyEPPO, 2014
PolandAbsent, confirmed by surveyEPPO, 2014
PortugalPresent, few occurrencesCABI/EPPO, 2012; EPPO, 2014
SpainPresent, few occurrencesDwinell, 1999b; CABI/EPPO, 2012; EPPO, 2014
UKAbsent, confirmed by surveyEPPO, 2014

Oceania

AustraliaAbsent, unreliable recordEPPO, 2014

Risk of Introduction

Top of page Pitch canker is a disease of great concern to countries where Pinus radiata is an important timber species. Thus quarantine restrictions are in force in New Zealand and Australia. Contaminated seed probably poses the greatest risk for introduction of the pathogen to new areas.

Hosts/Species Affected

Top of page The distinction drawn in the list of hosts between 'main' and 'other' hosts is somewhat arbitrary, and is based primarily on published reports of economic damage. The most important cultivated hosts are Pinus radiata, P. patula, P. elliotii var. elliotii, P. taeda and P. virginiana. Other hosts are less damaged because they are either: inherently less susceptible to the pathogen; exposed to lower disease pressure due to location, climate or levels of insect vector activity; or found in natural or less intensively managed systems. Further information on relative susceptibility of some of these hosts can be obtained from the literature (Dwinell, 1978; Dwinell et al., 1985; Storer et al., 1997; Guerra-Santos, 1999; Hodge and Dvorak, 2000; Gordon et al., 2001).

In addition to the species listed in the table, which have been observed to be naturally infected, a number of hosts have been discovered through artificial inoculations in the greenhouse or laboratory. These include Pinus contorta var. murryana, P. eldarica [P. brutia var. eldarica], P. jeffreyi, P. lambertiana and P. monophylla (McCain et al., 1987; Storer et al., 1994; Gordon et al., 1996, 1998a).

Growth Stages

Top of page Flowering stage, Fruiting stage, Pre-emergence, Seedling stage, Vegetative growing stage

Symptoms

Top of page When seedling mortality results from sowing infested seed, damping-off may occur prior to or after emergence. In the latter case, the fungus typically rots the hypocotyl at or near the soil-line and the seedling collapses. It is also possible for post-emergence infection to occur via cotyledons. This manifests itself as necrosis moving basipetally from the still-attached seed coat through the cotyledons towards the stem. Either avenue of infection occurs early in the life of the seedling, which may appear little different from a seedling killed by any number of other pathogens. Infection can also occur via soilborne propagules. Root infections are most often observed on seedlings in nurseries or Christmas tree farms, but can also occur on exposed roots of larger trees in landscape plantings. In Christmas tree farms, the pathogen may extensively colonize the root system, causing a brown discoloration and disintegration of the cortex. Above-ground symptoms are generally not apparent until the pathogen has reached the root crown and girdled the stem. This results in a uniform loss of colour in the foliage (see Pictures), which fades first to a dull green, then yellow and finally brown (dead). Pitching is evident on the main stem near the soil-line, and removal of the bark reveals a resin-soaked phloem/cambium/xylem with a honey-brown to dark-brown discoloration.

Pitch canker also causes symptoms through direct infections of branches and stems on trees of any age. This usually begins as branch dieback resulting from girdling at an infection site, which is often a cone node or non-cone branch whorl, but may also occur in inter-nodal regions. The earliest symptom is wilting of the needles distal to the infection site, which can be recognized by an accumulation of resin on the branch surface (see Pictures). Wilted needles lose their lustrous green colour and eventually become chlorotic, before turning red and finally brown; abscission tends to occur quickly and uniformly, leaving naked tips (see Pictures). The pace of this progression may vary depending on the season and the age of the infected branch. Early in the season, succulent branches may droop, giving the appearance of a shepherd's crook (see Pictures). Removal of the bark at an infection site reveals resin-soaked tissue with a brown discoloration. Individual infections do not progress very far axially along the infected stem, and their impact is typically limited to branch death distal to the infection. The disease intensifies through repeated infections (see Pictures), which can lead to extensive dieback in the canopy (see Pictures). Although initial infections are usually near branch tips, larger diameter branches and the main stem (trunk) of the tree may eventually sustain infections. This process accelerates the decline of the tree and girdling of the main stem often leads to top-kill and, in some cases, death of the entire tree. Infections on the trunk of the tree often produce copious amounts of resin which can coat large areas of the bark (see Pictures).

List of Symptoms/Signs

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SignLife StagesType
Fruit / abnormal shape
Fruit / discoloration
Fruit / reduced size
Growing point / dieback
Inflorescence / fall or shedding
Leaves / abnormal colours
Leaves / abnormal leaf fall
Leaves / wilting
Leaves / yellowed or dead
Roots / soft rot of cortex
Stems / canker on woody stem
Stems / dieback
Stems / gummosis or resinosis
Stems / internal discoloration
Stems / witches broom
Whole plant / discoloration
Whole plant / plant dead; dieback
Whole plant / seedling blight

Biology and Ecology

Top of page The teleomorph is readily formed under laboratory conditions and may occur in nature, but the anamorphic stage (Fusarium circinatum) predominates. Two asexual propagules, macroconidia and microconidia, are presumed to be the primary form in which the pathogen is disseminated, either by wind or by insects to which spores can adhere. Bark-feeding insects commonly breed in pitch canker-killed branches and a large percentage of the emergent brood carry the pathogen. These insects (including numerous species in the genera: Pityophthorus, Ips and Conophthorus) cannot only transport the pathogen to a new host but may also provide a wound suitable for infection and thus serve as vectors of pitch canker (Storer et al., 1997). These and other insects may also serve as wounding agents for fungal propagules already present on host surfaces.

The suitability of a wound for infection may depend on how rapidly it dries out. Thus, superficial wounds may require ambient moisture for an infection to occur, which could impose environmental constraints on the above-ground activity of the pathogen. Indeed, where the foliar phase of pitch canker is a problem, infections appear to be associated with locations/seasons where atmospheric moisture is readily available and temperatures are relatively warm, such as in the south-eastern USA during summer thunderstorms (Dwinell et al., 1985). In California, the disease is most severe in close proximity to the coast. The distribution of the disease also suggests that cooler temperatures are restrictive (Gordon et al., 2001). At moderate temperatures the pathogen survives for 1 year or more in infected wood. Spores can survive in soil for from several months to a year or more, depending on conditions. The climatic limitations on pitch canker are less likely to apply to the seedling phase of the disease, because conditions that are conducive to root growth in soil would generally also be suitable for infection by G. circinata.

Means of Movement and Dispersal

Top of page Natural Dispersal (Non-Biotic)

G. circinata produces spores that may become airborne, and these are presumably the primary propagules that are detected in air (Correll et al., 1991). Little is known about the limits of airborne dispersal but the pathogen is readily trapped out of the air in proximity to diseased trees and not in disease-free areas. These observations suggest that transport via air occurs over relatively short distances, but presumably longer range dispersal also occurs at a frequency that diminishes with distance from the source.

Vector Transmission

In California, many insects are known to carry the pitch canker pathogen, including pine-associated bark beetles (Coleoptera: Scolytidae) in the genera Pityophthorus, Ips and Conophthorus, and Ernobius (Coleoptera: Anobiidae). The pathogen has also been recovered from Lasconotus spp., beetles that are thought to be predatory, but it is not known if they are important as agents of dispersal. In the southeastern USA, Pissoides nemorensis and Rhyacionia spp. are suspected vectors and/or wounding agents. It seems likely that many as yet uncatalogued pine-associated insects will be found to carry G. circinata.

Silvicultural Practices

The pathogen can be moved with infected wood and further disseminated by insects that are carried within and later emerge from that wood. Contaminated pruning implements and infested soil on tools or vehicles also represent risks for transport of the pathogen. Pine litter (fallen needles) from infested areas (that might be used as mulch) is likely to harbour the pathogen and should not be moved into non-infested areas. Small diameter branches can be chipped to eliminate insects, but the pathogen survives this process (McNee et al., 2002). Debarking logs will eliminate most of the insects likely to carry the pathogen in this type of material.

Movement in Trade/Transport

The pathogen can be present in seed both externally and internally (Storer et al., 1998). Also, infected seedlings may show no symptoms.

Seedborne Aspects

Top of page Incidence

G. circinata can infest seed internally or be present as a superficial contaminant (Barrows-Broaddus and Dwinell, 1985; Storer et al., 1998). The mechanisms by which G. circinata infests seed are unknown. Superficial contamination might occur when airborne propagules enter the cone during periods when the cone is open. For cones on infected branches, fungal hyphae might grow from the lesion on the branch, through the cone stalk and into the seed. In Pinus radiata in California, the pathogen was isolated from up to 83% of seeds collected from cones on recently infected branches and from 21% of seeds from cones on symptomless branches (Storer et al., 1998). Seeds from symptomless branches were superficially contaminated, while up to 64% of seeds from recently infected branches were internally infested. The pathogen has similarly been isolated from seed of P. elliotii var. elliotii (Miller and Bramlett, 1979), P. taeda (Miller et al., 1984), P. palustris (Runion and Bruck, 1988), and P. echinata (Dwinell, 1999a).

Effect on Seed Quality

Internal infestations have been associated with deterioration of seed. Radiographs of infected seeds have shown the gametophyte shrunken from the seed coat and a slight deterioration of the embryo, while microscopy revealed hyphal growth and a lack of cellular organization of the seed tissues (Barrows-Broaddus and Dwinell, 1985). In a study of P. radiata, emergence from infested seed was reduced to 9%, down from 67% emergence from comparable uninfested seed (Storer et al., 1998). Similar levels of emergence have been observed for infested seed lots of P. palustris (Runion and Bruck, 1988).

Pathogen Transmission

Infection or contamination of seed may result in pre- or post-emergence damping-off or late season mortality of older, woody seedlings (Barnard and Blakeslee, 1980; Blakeslee et al., 1981; Storer et al., 1998).

Seed Treatments

For seeds that are only externally contaminated, the pathogen can be eliminated by soaking in 1% sodium hypochlorite for 2 minutes (Storer et al., 1998); 30% hydrogen peroxide has also been used for this purpose (Dwinell, 1999a). For seed that is infected internally, systemic fungicides have been used to increase emergence and reduce damping-off. Effective fungicides include thiabendazole-dimethyl sulfoxide (Runion and Bruck, 1988) and a formulated mixture of thiabendazole with carboxin and thiram (TR Gordon, University of California-Davis, USA, personal communication).

Seed Health Tests

The standard method by which G. circinata is detected on seed is by plating the seed on a Fusarium-selective medium (Correll et al., 1991). To discriminate between internal and external infections, half of the seed can be treated with sodium hypochlorite to eliminate external infections. After incubation of the plates for 5 days at approximately 20°C under a 12:12h fluorescent light regime, colonies are identified on the basis of colony morphology and size and shape of the microconidia and their disposition on the conidiophores (see section 'Morphology'). A different technique developed by Anderson (1986) utilizes blotter paper in conjunction with a nutrient medium semiselective for Fusarium. The broth contains 15 g peptone, 5 g MgSO4, 1 g KH2PO4, 0.75 g PCNB, 1 g streptomycin sulphate and 0.12 g neomycin sulphate in 1 L of distilled water. In this technique, the broth is sprayed onto steel-blue blotter paper until saturated. Twenty-five unsterilized seeds are evenly spaced on the blotter paper in a sterile, transparent, plastic box and crushed with a Plexiglas plate. The boxes are incubated at about 20°C until the colonies are about 2 cm in diameter (about 14 days) at which time the colonies are examined under the microscope. For seed lots judged to be pathogen-free by either of the above methods, confirmation should be obtained by conducting a seedling grow-out test. In this way, dormant seed infections not detected by culturing seed might be revealed.

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark hyphae; spores Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Flowers/Inflorescences/Cones/Calyx hyphae; spores Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Growing medium accompanying plants spores Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Leaves spores Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Roots hyphae Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Seedlings/Micropropagated plants hyphae Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Stems (above ground)/Shoots/Trunks/Branches hyphae; spores Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
True seeds (inc. grain) hyphae; spores Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Wood hyphae; spores Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope

Wood Packaging

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Wood Packaging not known to carry the pest in trade/transport
Loose wood packing material
Non-wood
Processed or treated wood
Solid wood packing material with bark
Solid wood packing material without bark

Impact

Top of page Pitch canker is a chronic problem in the south-eastern USA, where it affects production in plantations, nurseries and seed orchards. As such, it regularly adds to the cost of production but does not result in large financial losses in most years. Most southern pines are affected to some extent, including Pinus taeda, which typically sustains only minor damage and P. elliottii, which can be more severely affected. Major epidemics affected slash pine (P. elliottii) in Florida in the 1970s, with an estimated loss of between 13.6 and 30.7 million cubic feet annually in the period from 1974 through 1979 (Dwinell et al., 1985). The use of less susceptible genotypes and changes in silvicultural techniques have greatly reduced the impact since that time. In the south-eastern USA, pitch canker can also cause significant losses in pine seedling nurseries (Barnard and Blakeslee, 1980) and reduced cone yields in seed orchards (Dwinell et al., 1981; Dwinell et al., 1985).

Pitch canker is an important cause of damage and mortality of P. radiata in urban plantings and in native forests in California. Costs of tree removal and replacement may eventually amount to several million dollars in areas severely affected by pitch canker (Templeton et al., 1997). Pinus muricata and P. attenuata are also affected where native or planted trees are exposed to the pathogen.

Pitch canker has been a serious problem in seedling nurseries in South Africa (Viljoen et al., 1994); it is also found in nurseries in Chile and Spain, but the extent of the problem is not widely known. Pitch canker is apparently only a minor problem in Japan, but is perhaps more important in Korea (J Kim, University of Seoul, Korea, personal communication).

Environmental Impact

Top of page Pitch canker is primarily a problem in managed stands, where it does not impact on the natural environment. In native forests of Pinus radiata, pitch canker is of relatively recent occurrence (recognized in 1992), making it difficult to gauge its ecological impact. In areas where the disease is severe and fire is suppressed, pitch canker may promote conversion of a closed cone pine forest to oak woodland. Pitch canker is also found in native forests in Mexico, but significant ecological impacts have not been documented (Guerra-Santos, 1999).

Diagnosis

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Although the amber-coloured, resin-soaked appearance of tissue beneath the bark is a distinctive characteristic of pitch canker, isolation of the pathogen is strongly recommended to confirm a diagnosis. To make an isolation, pieces of wood are soaked in 70% ethanol for 30 sec and then in 1% sodium hypochlorite for 1 min. The pieces are blotted dry and placed on a Fusarium-selective (FS) medium (Correll et al., 1991) and incubated at room temperature. The composition of FS medium can be modified from the published recipe by eliminating the chlorneb, triadimefon, and rifampicin, and by reducing the pentachloronitrobenzene concentration from 750 ppm down to 200 ppm, without any apparent loss of selectivity. For species identification, candidate Fusarium colonies are transferred from FS medium to carnation leaf agar amended with 6.0 g/L of KCl (Fisher et al., 1983). In some areas, the occurrence of morphologically similar species can make definitive identification of the pathogen challenging (refer to the sections on 'Morphology' and 'Similarities to Other Species').

For the utmost confidence in a diagnosis, the isolate in question should be tested for pathogenicity to pine by mechanical inoculation (Gordon et al., 1998b). Additionally, differences in the sequence of the histone H3 gene can separate G. circinata from morphologically similar fungi (Steenkamp et al., 1999).

The detection and identification, via morphological and molecular methods, of the pathogen are described in OEPP/EPPO (2009).

Detection and Inspection

Top of page On living plants, pitch canker can be recognized as described in the Symptoms section. On raw logs, resinous cankers may be visible. Removal of the bark should reveal resin-soaked and discoloured wood. The pathogen can survive in chipped wood and would probably be difficult to detect from a visual inspection. The pathogen can also be transported as infested seed and in soil, and its presence in these materials would require laboratory tests to detect (see Diagnostic Methods section). Infected seedlings can be symptomless.

Similarities to Other Species/Conditions

Top of page Pre- and post-emergence damping-off caused by G. circinata is not readily distinguishable from death due to other seedling pathogens such as Pythium. Death of older seedlings (1-3 years of age), caused by G. circinata could be mistaken for Phytophthora root rot. Branch tip dieback caused by pitch canker is somewhat distinctive in the relatively rapid abscission of needles and the accumulation of resin at the junction of living and dead tissue (the infection site). The resulting naked tips, however, could be confused with symptoms caused by numerous other branch-infecting pathogens, such as Sphaeropsis sapinea and Peridermium harknessii [Endocronartium harknessii].

In the laboratory, it could be difficult to distinguish G. circinata from any of several species of F. subglutinans sensu lato; this includes F. guttiforme, F. pseudocircinatum, F. sacchari, F. subglutinans sensu stricto, and as yet undescribed species of Fusarium associated with mango and maize. All these taxa are similar in bearing microconidia in false heads but differ in a number of subtler characteristics that can be used to differentiate them from F. circinatum in most cases: whether condiophores originate directly from the substrate or from hyphae growing above the surface of the substrate; the number of conidiogenous openings per phialide; and the number of septa in the macroconidia.

Prevention and Control

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Due 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.

Phytosanitary Measures

Although the chemical seed treatments described in the section on 'Seedborne Aspects' may be effective in eliminating internal infections, such measures should not, by themselves, be considered sufficient to prevent transport of the pathogen. A more prudent policy would be to avoid movement of any pine seed from an infested region to areas where the disease does not occur. Likewise, movement of other pine material (logs, pine litter, wood chips, etc.) into uninfested areas should be avoided. These restrictions, if enforced, would significantly limit opportunities for introduction of the pathogen. For areas in the southern hemisphere where pines are not native, restrictions on the import of pine material would also aid in the exclusion of pine-associated insects which may not yet be present in an area. A host-free buffer zone around points of entry might be a useful measure, particularly in island nations such as New Zealand. A certification programme would be appropriate for seed orchards and pine nurseries. Such a programme might include visual inspection for symptoms and isolation from random samples. More importantly, nursery managers should be enlisted in a programme of continuous monitoring of seedling mortality, with representative samples sent to an appropriate diagnostic laboratory for testing.

Cultural Control and Sanitary Methods

Pruning to remove infected tips will usually not eliminate the disease, as pre-symptomatic infections will remain and new infections will continue to occur. However, if a lightly infected tree is relatively isolated from other diseased trees, removal of infected tips may slow the development of a new disease centre. Also, if elimination of infected branches can restore the aesthetic value of a tree and thereby allow it to be retained in the landscape, the cost of pruning may be repaid by a delay in removal and replacement of the diseased tree. Sterilization of pruning tools with Lysol or household bleach should be performed before and after pruning operations. Infected or uninfected cut branches and infected trees may contain or become infested with insects that carry the pathogen. Chipping this material will significantly reduce insect populations (McNee et al., 2002). If the chips are to be moved to an uninfested area, they should be further treated with moist heat (for example through composting or solarization) to eliminate the pathogen. It is not recommended that logs and firewood cut in infested areas be moved from the region of origin. If such logs must be moved, debarking is desirable because it will eliminate most of the habitat occupied by insects that can carry the pathogen and transmit the disease to healthy trees.

For Pinus radiata in California, USA, it is recommended that trees generally should not be removed solely due to pitch canker infection. Some trees, despite numerous infections, will remain relatively healthy due to genetic resistance. Others will become severely affected, but may later go into remission, a phenomenon which has been documented to occur at numerous locations (Gordon et al., 2001). A more aggressive approach to tree removal might be justified where an infected tree occurs in an area that is otherwise free of the disease.

In southeastern USA seed orchards and plantations, recommendations for cultural control consist of careful selection of a geographic location and planting site that are suitable for a particular species. When possible, it is suggested to use local seed sources which may be better adapted (Dwinell et al., 1985). In seed orchards, wounding incurred during harvest should be minimized. Over-fertilization should be avoided, as nitrogen fertilization in seed orchards may aggravate pitch canker problems (Fraedrich and Witcher, 1982). Maintaining clean seed orchards and seed production areas will reduce the potential for infected or contaminated seed.

In nurseries and Christmas tree farms, the use of clean seed is of paramount importance. When diseased seedlings or trees are found, they should be uprooted and either burned or placed in a sealed plastic bag for disposal. As much of the root system as possible should be removed. Because the fungus can be associated with soil, care should be taken not to distribute soil from the removal site to other locations on the farm. One should avoid the use of equipment that has recently been moved from an infested site. Because the pathogen may be present in areas where it has not yet been identified, using a high-pressure wash to remove soil before allowing any equipment on-site is a good precaution.

Host-Plant Resistance

In a large-scale inoculation study of Central American and Mexican pine species and Pinus radiata, 23 species, varieties, and geographic races were screened for resistance in a greenhouse (Hodge and Dvorak, 2000). In this study, P. radiata and its close relatives (Section Serotinae, sub-section Patula) were very susceptible (less than 10% surviving), while 4 out of 5 taxa in sub-section Oocarpa were extremely resistant. These resistant closed-cone species might be useful as alternate or secondary plantation species or as part of a hybrid breeding programme to improve resistance of P. radiata (Hodge and Dvorak, 2000).

Within P. radiata, variation in susceptibility has been observed in California populations of both planted and naturally regenerated trees (Storer et al., 1999; Storer et al., 2002). In native stands, management of pitch canker can best be achieved through practices that promote natural regeneration of the forest. Fire results in plentiful regeneration, and would also have the benefit of eliminating inoculum associated with the litter layer and the soil surface. The ability of P. radiata to colonize openings in the forest canopy will ensure regeneration in areas where gaps are created by any of various means, including pitch canker-induced mortality. Under these circumstances, selection in the presence of pitch canker should ultimately increase the frequency of resistant trees in the population. In managed stands, replanting with resistant seed or seedlings should be done as these materials become available.

Within several species of southern USA pines, there is documented variation in susceptibility. Disease severity can vary with the provenance of the host (P. elliotii; Dwinell and Phelps, 1977), between individual clones (P. taeda and P. virginiana; Kelley and Williams, 1982; Kuhlman et al., 1982; Barrows-Broaddus and Dwinell, 1984), or between full-sib or half-sib families (P. virginiana; Barrows-Broaddus and Dwinell, 1984). Among the recommendations to reduce incidence of pitch canker are the use of a local seed source, use of seed from resistant clones in existing orchards and continued selection for resistant material where feasible (Dwinell et al., 1985; Rockwood et al., 1988).

In landscape situations, non-pines or less susceptible pine species should be selected for planting in affected areas. For example, in California, several exotic pine species that are suitable for a Mediterranean climate are less susceptible than the native species (Gordon et al., 1998a).

Biological Control

No practical biological control programme exists for pitch canker. Although strains of a bacterium (Arthrobacter sp.) have been identified which are antagonistic to G. circinata in vitro, they were not found to control pitch canker in the field (Barrows-Broaddus et al., 1983; Barrows-Broaddus et al., 1985). Fusarium moniliforme [Gibberella fujikuroi] was found to be a competitive colonizer of wounds, making it a good candidate to protect wounds from infection. However, it is also a weak pathogen of seedlings (Dwinell et al., 1985).

Chemical Control

As is generally the case with diseases of trees, there are no realistic therapeutic options for dealing with pitch canker. Fungicides with activity against the pathogen are available, so, in principle, trees could be protected from infection. However, maintaining a sufficiently high concentration of the active ingredient on all susceptible surfaces would be problematic, even if cost were not a consideration. Therefore, in forest, landscape, and plantation situations, chemical control of pitch canker is not practised.

Chemical control might be feasible in more intensively managed systems such as nurseries and Christmas tree farms. Under nursery conditions, fungicides might be exploited to prevent infection of seedlings. For example, pre-plant treatment of Pinus palustris seeds with thiabendazole-dimethyl sulfoxide has been demonstrated to increase germination and seedling survival (Runion and Bruck, 1988). In a field trial in North Carolina, USA, treatment of 1-year-old P. taeda seedlings with thiabendazole reduced terminal shoot infections (Runion et al., 1993). Various biocidal treatments can be applied to the soil to eliminate the pathogen. On Christmas tree farms, the sites of diseased, removed trees should be treated to eliminate the pathogen from the soil. Broad-spectrum biocides such as metham sodium [metam] have been used for this purpose. When the treated site is eventually replanted, trees should be closely monitored for the appearance of pitch canker symptoms. If the disease reappears, the same procedure should be repeated.

The use of insecticides such as chlorpyrifos to control insect pests may indirectly reduce pitch canker infections by reducing the number of wounding agents and vectors (Dwinell et al., 1985; Runion et al., 1993). In general, however, chemical control of vectors would be economically unfeasible and not very effective. Furthermore, in some areas insect vectors are native pine associates that contribute to the process of decomposition.

References

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