POST HARVEST DISEASES OF CARROT

Post harvest diseases of carrotPost harvest diseases of carrot

Sour rot - Sour rot - Geotrichum candidumGeotrichum candidum Crown rot - Crown rot - Rhizoctonia solaniRhizoctonia solani Cottony soft rot - Cottony soft rot - Sclerotinia sclerotiarumSclerotinia sclerotiarum Phytophthora root rot - Phytophthora root rot - Phytophthora megaspermaPhytophthora megasperma Black rot - Black rot - Alternaria radicinaAlternaria radicina Root dieback - Root dieback - PythiumPythium debaryanum debaryanum Bacterial soft rot - Bacterial soft rot - Erwinia carotovoraErwinia carotovora sub sp. sub sp. caotovoracaotovora

Crown rot - Crown rot - Rhizoctonia solaniRhizoctonia solani

Damping-off of carrot seedlings and a crown rot later and during Damping-off of carrot seedlings and a crown rot later and during storagestorage

Field symptoms include premature senescence and death of foliageField symptoms include premature senescence and death of foliage

On carrot roots - dark brown sunken lesions or cankers near the On carrot roots - dark brown sunken lesions or cankers near the crown or in other parts of the root – crown or in other parts of the root – cavity spotcavity spot

FungusFungus Sclerotia - irregular, brown to black and 5mm in diaSclerotia - irregular, brown to black and 5mm in dia

Fungus produces both terminal and intercalary, barrel shaped Fungus produces both terminal and intercalary, barrel shaped chlamydosporechlamydospore

Hyphae of Rhizoctonia solani with right-angled branching pattern

Mode of spread and survivalMode of spread and survival R. solaniR. solani overwinters in soils as overwinters in soils as myceliamycelia on plant debris and as dark on plant debris and as dark

brown brown sclerotiasclerotia that remain in soil for long periods that remain in soil for long periods

R. solaniR. solani can spread from plant to plant in closely spaced carrots can spread from plant to plant in closely spaced carrots when the canopy is fully formedwhen the canopy is fully formed

EpidemiologyEpidemiology More severe on muck-grown carrots More severe on muck-grown carrots

Warm temperatures and wet conditions - especially when these Warm temperatures and wet conditions - especially when these environmental conditions occur near harvest environmental conditions occur near harvest

ControlControl Cultural practices that reduce crown injury and enhance soil Cultural practices that reduce crown injury and enhance soil

drainage and air circulation within the canopy are recommendeddrainage and air circulation within the canopy are recommended

Plant debris from previous crops should be removed before planting Plant debris from previous crops should be removed before planting carrotscarrots

Carrots should not follow perennial crops such as alfalfa Carrots should not follow perennial crops such as alfalfa

Quintozene – sprayed in the soil before sowing-effective controlQuintozene – sprayed in the soil before sowing-effective control

Cottony soft rot / white mould - Cottony soft rot / white mould - Sclerotinia sclerotiarumSclerotinia sclerotiarum

Foliage - water soaked, dark olive-green lesions associated with Foliage - water soaked, dark olive-green lesions associated with collapsed tissues collapsed tissues

Lesions expand rapidly over the entire leaf, petiole, and rosette with Lesions expand rapidly over the entire leaf, petiole, and rosette with infected tissuesinfected tissues

Covered by abundant cottony, white mycelium Covered by abundant cottony, white mycelium

Lesions of sclerotinia rot advancingon carrot petioles and the rosette

Collapsed leaves and petioles

At an advanced stage - affected tissues At an advanced stage - affected tissues exhibit a bleached appearance, and exhibit a bleached appearance, and occasionally an entire plant may collapse occasionally an entire plant may collapse

Large black sclerotia (2 to 20mm) form Large black sclerotia (2 to 20mm) form externally embedded in the mycelium or externally embedded in the mycelium or internally, within the pith of the petiole internally, within the pith of the petiole

Source of inoculum - soil - sclerotia, mycelium or ascospores of fungus Source of inoculum - soil - sclerotia, mycelium or ascospores of fungus occuroccur

Temp - 12.9 to 18.5Temp - 12.9 to 18.5ooCC

ControlControl Storage - Good ventilationStorage - Good ventilation

Use of clean containers, maintenance of temp near 0Use of clean containers, maintenance of temp near 0ooC and RH - 95%C and RH - 95%

Phytophthora root rot or rubbery brown rotPhytophthora root rot or rubbery brown rotPhytophthora megaspermaPhytophthora megasperma

Infected portions of the root become dark brown to black, water-Infected portions of the root become dark brown to black, water-soaked and rubbery in consistencysoaked and rubbery in consistency

Lesions may occur in one or more bands anywhere on the carrot Lesions may occur in one or more bands anywhere on the carrot root root

White mycelia may be present on lesions, which facilitates the White mycelia may be present on lesions, which facilitates the spread of the fungus to adjacent rootsspread of the fungus to adjacent roots

EpidemiologyEpidemiology Relatively wet soil conditions from excessive rain/irrigation and Relatively wet soil conditions from excessive rain/irrigation and

temperatures between 70 to 75ºFtemperatures between 70 to 75ºF

Mode of spread and survivalMode of spread and survival Soil borneSoil borne Produces zoospores (swimming spores) - easily spread through Produces zoospores (swimming spores) - easily spread through

water water

ManagementManagement Maintaining adequate soil drainage Maintaining adequate soil drainage Avoid prolonged periods of water saturation Avoid prolonged periods of water saturation Storage conditions - temperature at 32º F and RH <95%Storage conditions - temperature at 32º F and RH <95%

Black rot Black rot Alternaria radicinaAlternaria radicina

Seedling infection results in pre emergence and post emergence Seedling infection results in pre emergence and post emergence damping-off damping-off

Older senescing petioles on mature plants are particularly Older senescing petioles on mature plants are particularly susceptible to infection susceptible to infection

Provide an avenue for infection of the carrot crown, which appears Provide an avenue for infection of the carrot crown, which appears as a black ring of decay where the petioles attach to the root as a black ring of decay where the petioles attach to the root (black (black crown) crown)

Stored carrots - dry, black, sunken lesions which can decay the Stored carrots - dry, black, sunken lesions which can decay the entire root and spread to adjacent carrots entire root and spread to adjacent carrots

Mode of spread and survivalMode of spread and survival Seed borne Seed borne Survive in crop debris or in soil for up to eight years as spores spread Survive in crop debris or in soil for up to eight years as spores spread

via water and wind via water and wind Infects carrots at any stage of growth during periods of warm Infects carrots at any stage of growth during periods of warm

temperatures (greater than 68ºF) and extended leaf wetnesstemperatures (greater than 68ºF) and extended leaf wetness

ManagementManagement Cholorothalonil – Seed and soil applicationCholorothalonil – Seed and soil application Fungicides - Iprodione and StrobilurinsFungicides - Iprodione and Strobilurins > 8 years rotation with non host crop> 8 years rotation with non host crop Maintaining proper temperature and humidity (32ºF and 95% RH) in Maintaining proper temperature and humidity (32ºF and 95% RH) in

storagestorage Bacillus subtilis Bacillus subtilis && T. viride T. viride applicationapplication

Root dieback Root dieback PythiumPythium debaryanum, debaryanum, P. aphanidermatumP. aphanidermatum

Pythium brown rot and forkingPythium brown rot and forking

Root dieback of carrots produces excessively branched or stubbed Root dieback of carrots produces excessively branched or stubbed rootsroots

Fungus kills young tap roots after seed germination, reducing root Fungus kills young tap roots after seed germination, reducing root length and/or stimulating forkinglength and/or stimulating forking

Forking and stubbing occur, but these symptoms can also be Forking and stubbing occur, but these symptoms can also be caused by soil compaction, nematodes caused by soil compaction, nematodes

Mode of spread and survivalMode of spread and survival Produce sporangia and oosporesProduce sporangia and oospores

Spores and mycelia are responsible for the spread of the fungus in Spores and mycelia are responsible for the spread of the fungus in the field, which is facilitated by wet soil conditionsthe field, which is facilitated by wet soil conditions

Control Control Avoiding excessive wateringAvoiding excessive watering

By providing good field drainageBy providing good field drainage

Planting carrots in deep, friable and well drained soilsPlanting carrots in deep, friable and well drained soils

Post emergence fungicides - Mefenoxam - to control damping-off Post emergence fungicides - Mefenoxam - to control damping-off

Bacterial soft rot (Bacterial soft rot (Erwinia carotovoraErwinia carotovora sub sp. sub sp. caotovora)caotovora)

Cells become water soaked, middle lamella is destroyed and the Cells become water soaked, middle lamella is destroyed and the cells collapse cells collapse

Soft, watery or slimy consistency Soft, watery or slimy consistency

Rotted tissues – grey to brown, accompanied by foul odourRotted tissues – grey to brown, accompanied by foul odour

In the field, tops of rotted carrots turn yellow and wilt as roots break In the field, tops of rotted carrots turn yellow and wilt as roots break downdown

Bacteria Bacteria Gram –ve, motile with large peritrichous flagellaGram –ve, motile with large peritrichous flagella

Mode of survival and spreadMode of survival and spread Soil - source of primary inoculumSoil - source of primary inoculum Survive in decaying refuse and enter the root principally through Survive in decaying refuse and enter the root principally through

cultivation wounds, harvest bruises, freezing injury, and insect cultivation wounds, harvest bruises, freezing injury, and insect openingsopenings

Flies – Flies – Hylemus cillicrura, H. brassicae Hylemus cillicrura, H. brassicae – carry the bacteria in their – carry the bacteria in their intestinal tractsintestinal tracts

ControlControl Careful handling at harvest - minimizes bruising of carrot rootsCareful handling at harvest - minimizes bruising of carrot roots Washing - dipping in a solution of sodium hypochlorite (5.25%)Washing - dipping in a solution of sodium hypochlorite (5.25%) Storage condition - temp- just above freezing(0Storage condition - temp- just above freezing(0ooC), RH 90 %C), RH 90 % Crop rotation - alfalfa, beans, beets, cornCrop rotation - alfalfa, beans, beets, corn

Sour rot - Sour rot - Geotrichum candidumGeotrichum candidum

Soft, watery, colorless decay on carrot roots Soft, watery, colorless decay on carrot roots

Decayed area - covered with dull, white spores of the pathogen and Decayed area - covered with dull, white spores of the pathogen and a vinegar-like odour may developa vinegar-like odour may develop

Fungus - soil inhabitant that infects carrots through woundsFungus - soil inhabitant that infects carrots through wounds

In storage – warm temp (greater than 32°F) and improperly In storage – warm temp (greater than 32°F) and improperly ventilatedventilated

FungusFungus G. candidumG. candidum - grows as a series of filamentous cells called hyphae - grows as a series of filamentous cells called hyphae

Its spores, called conidia or arthrospores, are produced by Its spores, called conidia or arthrospores, are produced by fragmentation of the hyphaefragmentation of the hyphae

Hyphae and spores are white and appear colorless Hyphae and spores are white and appear colorless

ControlControl In the field In the field

• good field drainage good field drainage • minimizing wounding of carrotsminimizing wounding of carrots

In storage In storage • good sanitation (use of new or disinfected storage containers) good sanitation (use of new or disinfected storage containers) • precooling and storing carrots at 32º F is essentialprecooling and storing carrots at 32º F is essential

Crater rot-Crater rot- Rhizoctonia carotaeRhizoctonia carotaeSymptoms Symptoms Band of dark brown necrosis around the crown and horizontal brown canker-like lesions mostly on the crown and upper rootsBand of dark brown necrosis around the crown and horizontal brown canker-like lesions mostly on the crown and upper roots

Small pits subsequently developed beneath the lesions, that enlarged into sunken brown crater lines with a white, flocculent mycelium produced under high humiditySmall pits subsequently developed beneath the lesions, that enlarged into sunken brown crater lines with a white, flocculent mycelium produced under high humidity

Typical crater rot caused by R. caratoe on carrot roots. Note dark brown decay (arrows) around the crown and upper parts of the root.

BitternessBitterness• Carrots can develop off-flavours or bitterness in cool storage. The cause of these off-flavours is the production of compounds in carrots called isocoumarins. Isocoumarins develop when carrots are exposed to ethylene.Carrots can develop off-flavours or bitterness in cool storage. The cause of these off-flavours is the production of compounds in carrots called isocoumarins. Isocoumarins develop when carrots are exposed to ethylene.• Ethylene is a gas produced naturally by many fruits and vegetables, such as apples, bananas and tomatoes during ripening. Ethylene is a gas produced naturally by many fruits and vegetables, such as apples, bananas and tomatoes during ripening. • Carrots can be stored in sealed plastic bags in domestic refrigerators containing ethylene producing fruit.Carrots can be stored in sealed plastic bags in domestic refrigerators containing ethylene producing fruit.

Phenolic browningPhenolic browning• Phenolic browning (or surface browning) is seen as a browning or discoloration of the surface of carrot. Phenolic browning (or surface browning) is seen as a browning or discoloration of the surface of carrot. • It can develop when carrots are washed and stored in cool     rooms for long periods before packing.It can develop when carrots are washed and stored in cool     rooms for long periods before packing.•   Abrasion caused by mechanical washing often removes the epidermal layer (outer skin), exposing the carrot tissue to oxidation of phenolic compounds, which turn brown, or black in severe cases.Abrasion caused by mechanical washing often removes the epidermal layer (outer skin), exposing the carrot tissue to oxidation of phenolic compounds, which turn brown, or black in severe cases.• Phenolic browning can be confused with ‘5 o’clock shadow’ or boron deficiency of carrots. Phenolic browning can be confused with ‘5 o’clock shadow’ or boron deficiency of carrots. • The latter is seen as many small brown spots under the skin, causing the root to look dull.The latter is seen as many small brown spots under the skin, causing the root to look dull.

ManagementManagement Rapid removal of field heat.Rapid removal of field heat. Application of  Dowicide (Ophenylphenol) @ 98 g/L. Application of  Dowicide (Ophenylphenol) @ 98 g/L. 6 – methoxy mellen increase resistance6 – methoxy mellen increase resistance Cholorothalonil – Seed and soil application.Cholorothalonil – Seed and soil application. 8 years rotation with non host crop.8 years rotation with non host crop. Using disease free seed.Using disease free seed. Bacillus subtilis  Bacillus subtilis  && T.viride T.viride application.application.