Post harvest diseases of garlic

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Post harvest diseases of garlic

• White rot - Sclerotium cepivorum
• Blue mold rot - Penicillium spp.
• Black mould - Aspergillus niger
• Pink rot - Pyrenochaeta terrestis
• Internal bulb rot - Macrophomina phaseolina
• Basal rot - Fusarium oxysporum f. sp. garlic
• Neck rot - Botrytis allii

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White rot - Sclerotium cepivorum,s. rolfsii

• Leaves decay at the base, turn yellow, wilt, and
  topple over
• Roots and bulbs - covered with a fluffy white
  mycelium
• Affected bulbs may become watery, and the outer
  scales crack as the bulb dries and shrinks
• Small black sclerotia form on and in affected
  bulb parts

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• Mode of spread and survival
• Cool weather - needed for germination of
  sclerotia and hyphal growth
• Mycelium - encounters a host root, the fungus
  will form appresoria
• Mycelium can grow outwards from the roots of one
  plant to the roots of a adjacent plant
• Control
• Rotating out of Allium crops for ten years
• Destroying infected tissue
• Planting disease - free seed stock
• Seed dressing with benomyl or carbendazim(100-150g
  /kg of seed)

Micro sclerotia of the White Rot fungus
S.cepivorum developing on an infected garlic bulb
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Basal rot - Fusarium oxysporum f. sp. garlic

• Plants - show reduced emergence, yellowing and/or
  browning (necrosis) of leaves beginning at tips
• Reduced bulb size, bulb decay, and brown, poorly
  developed root systems
• In storage - bulbs show spongy, sunken, yellow
  brown rotting lesions

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• In early stages - infected bulbs are softened,
  brown and watery when cut open
• White, light pink or reddish fungal growth
  covering the cloves or in rot cavities
• Deep cracks form in the cloves, followed by break
  down of the tissue, which will eventually dry
  down to a portion of its original size, the
  cloves becoming crinkled and small

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• Disease Cycle
• Soil borne fungus and can persist for long
  periods in the soil
• Transmission - infested soil on tools or
  equipment, infected debris, infected seed, or
  run-off water
• Pathogen enters the plant through wounded tissue
• Disease develops from the base of the bulb and
  progresses towards the tips of the cloves
• Favored by higher RH and temperatures(20-30oC)

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• Management
• Avoid rotations with Allium spp.(e.g. onions and
  leeks) and cereals
• Store bulbs at cool temperatures and low humidity
  with good ventilation
• Avoid storing damaged bulbs

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Blue mold rot - Penicillium spp.

• A blue-green color powdery mould is observed on
  cloves in soil and in storage, thus its common
  name, Blue Mold
• Air-borne spores spread the disease
• Infection first occurs on wounds sustained when
  cloves are separated from the parent bulb
• CONTROL
• Bulbs are harvested carefully to avoid wounds and
  bruising, then promptly dried or cured

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Black mould (Aspergillus niger and A. alliaceous)

• Whole tissue become black powdery mass
• Individual bulbs shrivel and become light in
  weight
• Under high humid condition the inner tissues
  become moderately soft
• Infected bulbs lose their pungency and smell
• Rotten garlic cloves show black, brown, pink or
  white coloured rotting

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• Fungus
• Mycelium - branched, septate thick walled foot
  cells differentiate and give rise to a single
  conidiophore
• Conidiophore - globose on which brown sterigmata
  are formed
• Vesicle, sterigmata, conidia make up the black
  head - characteristic of the fungus
• Control
• Rapid and thorough curing
• Storage - good ventilation
• Temp - just above 0oc

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Pink rotPyrenochaeta terrestis

• Roots are affected and they turn pink or reddish
  and sometimes darken to a red or purple colour
• Black spores form on the diseased roots which
  eventually shrivel and die
• Pathogen - Soil borne and infection is mostly
  from mycelia in the soil
• Temp - 24-28oc

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Internal bulb rot - Macrophomina phaseolina

• No external symptom can be observed unless the
  outer scales are removed
• Black pin head microsclerotia develop over the
  fleshy scales which are light in weight, brown,
  mostly shrivelled
• Do not lose their pungency
• Control
• Dipping of bulbs in formalin 0.03
• Boric acid-2.0

After harvest to minimize storage rot
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Neck rot - Botrytis allii

• Found upon the bulbs at the time of harvest
• Affected scale tissue become soft
• Dense layer of grey mould appear at the neck
• Infection progresses most rapidly down the scales
  which have been originally infected

Garlic with neck rot
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• Mode of spread and survival
• Survive as sclerotia
• Requires cool and moist weather
• Temp -15 to 20oc
• Control
• Promoting rapid drying at harvest and good
  aeration in storage is best for managing Botrytis
  on bulbs
• Additionally, cooler storage temperatures may
  help control the disease