Garlic

advertisement
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
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
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
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

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
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)
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
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
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
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
Pink rot
Pyrenochaeta 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
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
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
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
Download