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ONION Neck Rot - Botrytis allii Neck Rot - Botrytis allii Blue Mould Rot - Penicillium spp Blue Mould Rot - Penicillium spp White rot - Sclerotium cepivorum.

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Presentation on theme: "ONION Neck Rot - Botrytis allii Neck Rot - Botrytis allii Blue Mould Rot - Penicillium spp Blue Mould Rot - Penicillium spp White rot - Sclerotium cepivorum."— Presentation transcript:

1 ONION Neck Rot - Botrytis allii Neck Rot - Botrytis allii Blue Mould Rot - Penicillium spp Blue Mould Rot - Penicillium spp White rot - Sclerotium cepivorum White rot - Sclerotium cepivorum Bulb rot/ basal rot - Fusarium oxysporum f.sp. cepae Bulb rot/ basal rot - Fusarium oxysporum f.sp. cepae Macrophomina rot - Macrophomina phaseoli Macrophomina rot - Macrophomina phaseoli Purple blotch - Alternaria porri Purple blotch - Alternaria porri Black stalk rot -Stemphylium botryosum Black stalk rot -Stemphylium botryosum Black mould - Aspergillus niger Black mould - Aspergillus niger

2 Neck Rot - Botrytis allii Latent disease - although infection takes place in the field Latent disease - although infection takes place in the field Softening of scales which take on a water soaked appearance Softening of scales which take on a water soaked appearance Under moist conditions - greyish sporulating mycelial mat develops on the surface of the scales Under moist conditions - greyish sporulating mycelial mat develops on the surface of the scales

3 Mode of spread and survival Fungus persists saprophytically on dead onion tissue, on humus in soil and as sclerotia near the surface of previous onion crop cells Fungus persists saprophytically on dead onion tissue, on humus in soil and as sclerotia near the surface of previous onion crop cells Sclerotia germinate in moist weather and produce conidia that are disseminated by air currents Sclerotia germinate in moist weather and produce conidia that are disseminated by air currents When conidia land on the onion necks that are cut or wounded they can geminate, penetrate and kill onion tissue When conidia land on the onion necks that are cut or wounded they can geminate, penetrate and kill onion tissue

4 Control Dusting the seed with benomyl at 1g/kg of seed Dusting the seed with benomyl at 1g/kg of seed Avoid excessive and late (after mid-July) applications of nitrogen Avoid excessive and late (after mid-July) applications of nitrogen Rapid and thorough drying directly after harvest Rapid and thorough drying directly after harvest Provide good ventilation for curing onions before storage Provide good ventilation for curing onions before storage

5 Blue Mould Rot - Penicillium spp. Blue Mould Rot - Penicillium spp. Initial symptoms - water soaked areas on the outer surface of scales Initial symptoms - water soaked areas on the outer surface of scales Later, a green to blue green, powdery mould may develop on the surface of the lesions Later, a green to blue green, powdery mould may develop on the surface of the lesions Infected areas of fleshy scales are tan or grey when cut Infected areas of fleshy scales are tan or grey when cut In advanced stages, infected bulbs may disintegrate into a watery rot In advanced stages, infected bulbs may disintegrate into a watery rot

6 Penicillium digitatum, P. oxalicum, P. expansum, P. luteum Penicillium digitatum, P. oxalicum, P. expansum, P. luteum Produces enormous number of spores on a broom like conidiophore Produces enormous number of spores on a broom like conidiophore Saprophytes on plant debris and senescent plant tissue Saprophytes on plant debris and senescent plant tissue Invasion - through wounds, bruises, or uncured neck tissue Invasion - through wounds, bruises, or uncured neck tissue Optimum conditions include moderate temperatures (21° to 25°C) and high relative humidity Optimum conditions include moderate temperatures (21° to 25°C) and high relative humidity

7 Management Avoid wounds and insect damage to bulbs Avoid wounds and insect damage to bulbs Harvest and handle onion bulbs with a minimum of bruising or wounding Harvest and handle onion bulbs with a minimum of bruising or wounding Cure the bulbs so the necks are dry Cure the bulbs so the necks are dry Store bulbs at temperatures of 41°F (5°C) or less with low relative humidity Store bulbs at temperatures of 41°F (5°C) or less with low relative humidity

8 White rot / mouldy nose/ Dry rot (Sclerotium cepivorum) Leaves - yellow and dieback Leaves - yellow and dieback Roots - rotten & base of the bulb covered with a watery or grey fungal growth Roots - rotten & base of the bulb covered with a watery or grey fungal growth Numerous small black spherical sclerotia are produced Numerous small black spherical sclerotia are produced

9 Mode of spread and survival Sclerotia persists in soil for eight years Sclerotia persists in soil for eight years Pathogen has no direct sporulation stage and it is not air borne Pathogen has no direct sporulation stage and it is not air borne Sclerotia are transported from field to field by flood water Sclerotia are transported from field to field by flood waterManagement Long rotation of 8 to 10 yrs Long rotation of 8 to 10 yrs Good drainage Good drainage Use of healthy planting materials Use of healthy planting materials Destruction of wild onion and leeks Destruction of wild onion and leeks Seed dressings-benomyl/carbendazim Seed dressings-benomyl/carbendazim

10 Bulb rot/ basal rot (Fusarium oxysporum f.sp. cepae) Bulb rot/ basal rot (Fusarium oxysporum f.sp. cepae) Occur in patches Occur in patches Leaves - turn yellow and then dry up slowly Leaves - turn yellow and then dry up slowly Entire plant shows complete drying of the foliage Entire plant shows complete drying of the foliage Bulb - shows soft rotting and the roots get rotted Bulb - shows soft rotting and the roots get rotted Whitish mould growth on the scale Whitish mould growth on the scale

11 Fungus Produces many chlamydospores which are thick walled resting spores Produces many chlamydospores which are thick walled resting spores Microconidia – one celled and thin walled Microconidia – one celled and thin walled Mode of spread and survival Soil borne Soil borne Infection occurs through root, either directly or through wounds Infection occurs through root, either directly or through wounds Soil insects are common carriers Soil insects are common carriers Macroconidia Fusarium sp

12 Epidemiology High temp and low level of soil moisture - favourable for high disease incidence High temp and low level of soil moisture - favourable for high disease incidence Temp- 28 to 32 o c Temp- 28 to 32 o cManagement Field sanitation - destruction of infected plant debris Field sanitation - destruction of infected plant debris Soil drenching - COC-0.25% Soil drenching - COC-0.25% Pre planting treatment of bulbs - benomyl 15%+ mancozeb 60% Pre planting treatment of bulbs - benomyl 15%+ mancozeb 60% Local Bellary, Poona Red Globe, Patna Red, White Large - resistant varieties Local Bellary, Poona Red Globe, Patna Red, White Large - resistant varieties

13 Black stalk rot (Stemphylium botryosum) Affects garlic and leek Affects garlic and leek Attacks only diseased, injured bulbs and aging tissue Attacks only diseased, injured bulbs and aging tissue Damage by weakening the seed stalks when they are almost ripe causing them to break over Damage by weakening the seed stalks when they are almost ripe causing them to break over Spoil the appearance of the bulb with a sooty mould before they are marketed Spoil the appearance of the bulb with a sooty mould before they are marketed The fungus Stemphylium botryosum growing and sporulating on top of a downy mildew lesion

14 Fungus Producing short clavate to cylindrical asci in brown pseudothecia Producing short clavate to cylindrical asci in brown pseudothecia Ascospores yellow to yellowish brown, oval to ellipsoid, x um with 1-5 vertical and 7 transverse septa Ascospores yellow to yellowish brown, oval to ellipsoid, x um with 1-5 vertical and 7 transverse septaControl Harvest without causing any bruises Harvest without causing any bruises Bulbs should be dried properly before storage Bulbs should be dried properly before storage Conidia - Stemphylium botryosum

15 Purple blotch /scald disease Alternaria porri Leaves - whitish minute dots on leaves with irregular chlorotic areas on tip portion Leaves - whitish minute dots on leaves with irregular chlorotic areas on tip portion Circular to oblong concentric black velvety rings appear in chlorotic area Circular to oblong concentric black velvety rings appear in chlorotic area Lesions develop towards the base of the leaves Lesions develop towards the base of the leaves Leaves die from the tip downwards, break at the point of infection and hang down Leaves die from the tip downwards, break at the point of infection and hang down Bulbs – semi watery rot, shrinkage of the fleshy bulb scales and desiccation followed by these scales becoming dry and papery Bulbs – semi watery rot, shrinkage of the fleshy bulb scales and desiccation followed by these scales becoming dry and papery

16 Fungus Mycelium - branched, coloured and septate Mycelium - branched, coloured and septate Conidiophores - singly or in groups, septate, pale to mid brown Conidiophores - singly or in groups, septate, pale to mid brown Conidia - solitary, straight or curved Conidia - solitary, straight or curved Mode of spread and survival Carried through seed bulbs collected from infected field Carried through seed bulbs collected from infected field Spreads mainly through air borne spores Spreads mainly through air borne spores Pathogen enters through stomata or wounds Pathogen enters through stomata or wounds Survives in plant debris for 8 months Survives in plant debris for 8 months Conidia Conidium

17 Epidemiology Temp - 21 to 30 o c Temp - 21 to 30 o c RH - 90 % RH - 90 %Management Seed treatment - 2.5g/kg of seed Seed treatment - 2.5g/kg of seed Three sprays of, Three sprays of, Copper oxychloride %Copper oxychloride % Chlorothalanil - 0.2%Chlorothalanil - 0.2% Zineb - 0.2%Zineb - 0.2% Mancozeb - 0.2% Mancozeb - 0.2% Varieties - New Selection, Red Creole - resistant Varieties - New Selection, Red Creole - resistant

18 Black mould - Aspergillus niger Masses of black powdery spores on both exterior and between the scales of the bulbs Masses of black powdery spores on both exterior and between the scales of the bulbs Especially along the vascular strands of the veins Especially along the vascular strands of the veins

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

20 Macrophomina rot Macrophomina phaseoli Rotting of onion in storage Rotting of onion in storage Diseased bulbs become ashy Diseased bulbs become ashy Close examination shows – dark charcoal coloured blemishes on one or two scales below the outer papery scale Close examination shows – dark charcoal coloured blemishes on one or two scales below the outer papery scale Many pin head size sclerotia- embedded in affected tissues Many pin head size sclerotia- embedded in affected tissuesControl Dipping bulbs in formalin 0.03% or boric acid 2.0% Dipping bulbs in formalin 0.03% or boric acid 2.0%


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