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 Micro sclerotia of the White Rot fungus

S.cepivorum

developing on an infected garlic bulb Seed dressing with benomyl or carbendazim(100-150g/kg of seed)

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(20-30 o C)

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 0 o c



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 - 24-28 o c

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 20 o c 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