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Post harvest diseases of garlic

Post harvest diseases of garlic

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Post harvest diseases of garlic

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  1. Post harvest diseases of garlic White rot - Sclerotiumcepivorum Blue mold rot - Penicilliumspp. Black mould - Aspergillusniger Pink rot - Pyrenochaetaterrestis Internal bulb rot - Macrophominaphaseolina Basal rot - Fusariumoxysporum f. sp. garlic Neck rot - Botrytis allii

  2. White rot - Sclerotiumcepivorum,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

  3. Micro sclerotia of the White Rot fungus S.cepivorum developing on an infected garlic bulb 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)

  4. Basal rot - Fusariumoxysporum 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

  5. 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

  6. 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)

  7. 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

  8. Blue mold rot - Penicilliumspp. • 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

  9. Black mould (Aspergillusniger 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

  10. 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

  11. Pink rotPyrenochaetaterrestis 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

  12. Internal bulb rot - Macrophominaphaseolina After harvest to minimize storage rot • 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%

  13. Neck rot - Botrytis allii Garlic with neck rot 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

  14. 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