Post harvest diseases of citrus

Dr. P. Kishore Varma

Assistant professorPJTSAU, Hyderabad

Green and blue mold – Penicillium spp.

Green mold

• Penicillium digitatum (green mould)

• P. italicum (blue mould)• Softening of damaged

tissue.• White fungal growth,

which progressively turns blue or green as spores develop.

• Infections develop from damaged areas.

• The growth of mould increases with storage

• Optimum temperatures (20-270C).

• Late season fruit more susceptible.

• Damaged rind is more susceptible.

3Blue mold

Green and blue mold – Penicillium spp.

Pathogen biology – Penicillium digitatum

Penicillium digitatum

Penicillium italicum

Sour rot - Geotrichum candidum / G. citri-aurantii

• Very soft, watery decay.

• Distinct margin between

decayed and healthy tissue.

• Lesions covered with slimy

off-white spores

• Sour odour detectable.

• Prevalent after warm wet areas

• Pathogenic on ‘weak’,

wounded, bruised, and split fruit

• Lemons, limes and grape fruits stored for extended periods

• Ripe fruit is more susceptible

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Geotrichum candidum

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Stem end rot - Lasiodiplodia theobromae

• Softening of tissue around button

• Brown rind with dark flesh beneath

• Rapid decay down the axis of the fruit reaching stylar end

• Abundant rainfall during crops eason

• Ethylene degreening treatments predispose fruit to Botryodiplodia infection

• Quiesecent in floral remnants under the sepals of fruit

• Botryodiplodia – 300C • Phomopsis, Dothiorella -

230C

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Botryodiplodia theobromae

Phomopsis citri

Dothiorella

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Brown rot - Phytophthora citrophthora

• Greyish brown firm and leathery spot

• Pungent odour• Fine white spore bearing

mould on peel• Develops rapidly at - 250C

Phytophthora citrophthora, P. citricola, P. hibernalis

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Anthracnose - Colletotrichum gloeosporioides

Tear stain

• Superficial leathery

appearance

• Silver/grey to dark lesions.

• Tear-staining pattern

• Pink tinge (spores) under

humid conditions.

• Infection occurs by rain-splash during autumn.

• ethylene degreening increases sensitivity to anthracnose

• Quiescent - appressoria

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Colletotrichum gloeosporioides

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Trichoderma rot - Trichoderma viride

• Peel turns dark brown• Veins on the interior

surface of the peel turn brown

• Odour of coconuts• Yellow green to dark

green sporulation on surface

Trichoderma viride

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Management• Careful handling• Sanitation• Sodium-ortho phenyl phenate, sodium carbonate

• Benzimidazole and imazalil• Curing citrus fruits at 360C for 3 days• Yeast, eg. Debaryomyces, Pichia

• Candida famata, Pseudomonas syringae, Aureobasidium pullulans

• Aspire – Candida oleophila• Biosave – P. syringae

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Management

• Stem end rots – TBZ, Benomyl, Imazalil, prochloraz

• Brown rot – Fixed copper fungicides, Metalaxyl, Fosetyl-Al

• Hot water dip treatments at 46-490 C for 3 min• Stem-end rots – Refrigeration between 4-70 C • Anthracnose- <100 C

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Citrus disorders

Chilling injury• Critical temperature – 10-150C for grapefruit,

lemons and lime• 1 and 50C – Oranges, mandarins

• Brown pitting of rind• Watery breakdown• Brown staining of peel or peel tissue collapse• Oil gland darkening – grapefruits• Albedo browning, membranous stain - lemons

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Chilling injury

• Abnormal biochemical changes• Moisture loss from peel• Growth regulators and fungicides

• Varies from season to season

Chilling injury vs. Pitting

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Peel tissue collapseDevelops in 4-6 weeks in storageReduced by waxing

Oil gland targetedDevelops in 3-4 daysCaused by wax application

Chilling injury-Management

• Reduction of moisture loss by applying oil, wax (shellac) or film

• Maintain high humidity• Sealing in polyethylene film• Pre-conditioning of fruits to chilling temperatures• Intermittent heating• Fungicide application (eg. TBZ)

• Low oxygen and high CO2

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Optimal temperature with proper wax is the best means for controlling chilling injury

Freezing injury

• Temperature below -1.50C

• Browning of peel

• Water soaked membranes between the segments

• Mandarins- crystals in pulp

• Grapefruit – milky appearance of pulp

• Cavities in flesh

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Oleocellosis or rind-oil spotting

• Common on lemons and limes• Injured areas firm, irregular in shape• Yellow, green or brown discolouration

• Oil glands appear prominent

Reasons• Compression of fruits

• Sudden spell of cold weather• Physical injury to the peel• Fruits harvested in cool, wet periods

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Oleocellosis

Management• Pre-harvest spray of ethylene• Avoid harvesting immature turgid fruits

• Avoid picking too early in the season

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Other disorders

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Creasing Chemical injury

Peteca Puffiness