Stem canker disease of Hopea odorata Roxb.

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Stem canker disease of Hopea odorata Roxb. in
southeastern region of Viet Nam
Pham Quang Thu Forest Protection Research
Division Forest Science Institute of Vietnam
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Main content

• Present situation
• Disease symptom
• Causal organism
• Distribution
• Pathology
• Disease impacts
• Disease control and management

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Present situation

• Hopea odorata Roxb. is distributed naturally in
  some provinces of the southern part of Viet Nam.
• It grows in dense tropical rain forests,
  producing high quality and economically valuable
  timber.
• Hopea odorata Roxb. is currently being chosen as
  the main species for forest rehabilitations in
  state-owned forest enterprises, such as Ma Da, La
  Nga, Tan Uyen, Tan Phu, Xuyen Moc and Vinh An in
  southeastern region of Vietnam.

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Present situation

• In 2002, a disease known as die back occurred
  for the first time in Vietnam and caused
  significant impact on the growth of Hoppea
  odorata plantations in several locations,
  especially in Tan Uyen and Vinh An.
• Disease symptom tends to spread to other
  locations.

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Disease symptom

• Cankers and dead areas of bark sometime with
  sunken lesions extending from a few centimeters
  to more than a meter along branches and stem
  axes. They may be darkly discolored and cracked.
• Branches and stems may be partially or
  completely girdled, leading to crown die back and
  possibly tree death.

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Disease symptom
Diseased plantation
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Disease symptom

• Cankers are often associated with wounds, borer
  damage or branch stubs.
• Wood of stems or branches infected by pathogen
  become to discoloration

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Disease symptom
Discoloration of wood of infected stem
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Causal organism

• The fruiting bodies of the causal fungus can
  usually be found on the cankers themselves at the
  margin between the diseased and the healthy bark
  or the newly dead areas.
• Fruiting bodies are typically partially
  submerged in the outer bark but can be readily
  seen through a hand lens
• Dimension of the fruiting bodies is from 0.5 to
  0.7 mm.

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Causal organism
Acsi of causal fungus contains 8
ascosprores, Asci is about 240 µm in length and
25 µm in wide Ascospore is about 30 µm in length
and 15 µm in wide
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Causal organism
immature ascospores
Mature ascospores
Immature ascospores are light brown color Mature
ascospores are dark brown color
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Causal organism
Oil drop
Septum
Ascospores have one septum divided the ascospores
into 2 cells. There are usually a oil drop in one
cell or both cells of mature ascospores
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Source Ken Old, 2000
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Causal organism

• The pathogenic fungus was identified to be
  Macrovalsaria megalospora (Mont) Sivan.
• This fungus also associated with stem canker on
  Acacia mangium in various southeastern regions of
  Vietnam.
• The fungus was considered to be weak pathogen to
  A. mangium in Vietnam (Ken Old, 2000).

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Causal organism

• There was other fungus which was considered to
  be an opportunist pathogen of stressed trees of
  Hopea odorata.
• The fruiting bodies of the fungus completely
  submerged in the outer bark, columns of mass
  conidia of an opportunist pathogen came out the
  bark in moist conditions.

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Causal organism
Columns of mass conidia of opportunist pathogen
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Causal organism
Conidia of opportunist pathogen
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Distribution

• The fungus Macrovalsaria megalospora are mainly
  found in the tropics and sub-tropics.
• In Vietnam this fungus is pathogen of both
  Acacia mangium and Hopea odorata.
• Distribution of this fungus is only found in
  only some locations in the southeastern region of
  Vietnam.

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Pathology

• Trees planted in infertile soils and drought
  areas are usually infected by this fungus.
• Trees damaged by insects, stems borers are more
  susceptible to attack by canker fungus
  Macrovalsaria megalospora.
• Poor silvicultural operations resulting in stem
  wounds predispose trees to infection
• The pathogens enter to stem tissue through
  wounds. They kill cambial tissue and sapwood.

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Pathology

• Disease incidence and disease severity vary in
  locations, depending probably on host
  susceptibility and local environmental
  conditions.
• Acacia mangium plantations as sources of
  inoculum for the pathogens have been recognized.
• Disease incidence of stem canker on Hopea odorata
  was found to be higher in plantations where
  infected A. mangium trees were present.

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Disease impacts

• The main impacts is loss of stems and leading
  shoots.
• Very severe die back symptom was reported in a
  Hopea odorata plantation of Tan Uyen forest
  enterprise, with up to 30, where the Hopea
  odorata plantation was very close to infected A.
  mangium plantations with Macrovalsaria
  megalospora fungus.
• Die back symptom was more higher, with up to 40
  when Hopea odorata trees were interplanted with
  infected A. mangium trees in Vinh An forest
  enterprise.

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Control and management

• The only feasible control is through good
  avoidance of stress through good silviculture
  (spacing and thinning).
• The best strategy for control and management of
  the disease would be early recognition of the
  disease followed by removal and infected trees
  and branches.
• Avoidance of wounds will reduce entry point for
  pathogens.

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Control and management

• In the long term, selection at the provenance
  level for disease resistance may avoid
  significant disease incidence.
• It would be better do not planting Hopea odorata
  seedlings close to Acacia mangium plantations
  infected by Macrovalsaria megalospora.

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