EFFECT OF PREHARVEST FACTORS ON

POSTHARVEST QUALITY

John P Bower

Consultant: Horticultural Product Quality

Will focus on

Mineral nutritionMineral nutrition

Water relations Water relations irrigationirrigation

Consider the effects on

Fruit ripeningFruit ripening

Shelf life and storage capabilityShelf life and storage capability

External and internal disordersExternal and internal disorders

Potential shelf life and quality determined by

Physiological Physiological condition at condition at harvestharvest

Important because

At harvestAt harvest

Cut off water supplyCut off water supplyCut off new carbohydrate supplyCut off new carbohydrate supply

Postharvest

Cells need to continue livingCells need to continue livingNeed energyNeed energyMust be sufficiently hydratedMust be sufficiently hydrated

Apply stress (low temperatures, Apply stress (low temperatures, water loss)water loss)

Cells must be robust (membranes)Cells must be robust (membranes)Need sufficient antiNeed sufficient anti--oxidantsoxidants

How does

Mineral nutritionMineral nutrition

Water relations (irrigation)Water relations (irrigation)

Affect these factors?Affect these factors?

MINERAL NUTRITION

Mineral nutritionMay be complexMay be complex

Macro and micro elements Macro and micro elements involvedinvolved

Interactions may take placeInteractions may take place

However, certain elements stand However, certain elements stand outout

CalciumConsidered important for many fruit Considered important for many fruit including avocadoincluding avocado

Stabilizes membranesStabilizes membranes

Structural component of cell wallsStructural component of cell wallsAffects rate of ripeningAffects rate of ripening

Higher calcium known to be linked to Higher calcium known to be linked to fewer internal disordersfewer internal disorders

Calcium

South African exporters use fruit South African exporters use fruit Ca as a quality prediction factorCa as a quality prediction factor

Found values of > 1000mg kgFound values of > 1000mg kg--1 1 in in November (end of main cell November (end of main cell division)division)

Calcium uptake

Spray applications variable, not Spray applications variable, not very usefulvery useful

Need to consider natural uptake Need to consider natural uptake to fruitto fruit

Calcium concentration changes

Weeks after petal fall

Concentration m eq 100g DM-1

End of major cell division

Factors affecting calcium uptake

Cell divisionCell division

AuxinAuxin movementmovementTested with Tested with auxinauxin blocker (TIBA)blocker (TIBA)

Experiment to show auxin effect

Agar + Ca45

Fruit

Agar + Ca45

TIBA

Agar + Ca45

Auxin

Ca45 Auxin

Therefore

Areas of major cell divisionAreas of major cell division

Areas exporting most Areas exporting most auxinauxin

Get preference for calciumGet preference for calcium

Other factor of importance

Water movementWater movement

Ca moves in xylem with water flowCa moves in xylem with water flow

Therefore transpiration importantTherefore transpiration important

Water and therefore Ca affected by supply

Weeks after petal fall

Auxin and water movement also affected by

Reproductive to vegetative Reproductive to vegetative growth ratiogrowth ratio

Vegetative growth

Difficult to modify timingDifficult to modify timing

Can modify vigourCan modify vigour

Greatest driver of vegetative growth

NitrogenNitrogen

Therefore not surprisingNitrogen found most important Nitrogen found most important element forelement for

Postharvest quality (Postharvest quality (MesocarpMesocarpdiscoloration)discoloration)

Observed effects of nitrogen

Low nitrogen High nitrogen

Main fruit mineral elements contributing to mesocarp discoloration

Nitrogen 38.1%Copper 28.1%Manganese 12.3%Boron 7.9%Calcium 3.0%

For managementNN22 much more important than Camuch more important than CaFix Ca allocation byFix Ca allocation by

Managing vegetative vigourManaging vegetative vigourLimit NLimit N22 during critical fruit growth during critical fruit growth stagestage

South African exporters use:South African exporters use:NN22 < 1% in January as quality index< 1% in January as quality index

Importance of carbohydratesImportance of carbohydrates

Needed to driveRespiration

Affects shelf lifeNormal ripening

Main carbohydratesMannoheptulosePerseitol

Mannoheptulose

More than one function

Energy

Possible role in ripening

Powerful anti-oxidant

Therefore important for quality

Carbohydrates in fruit affected by

Total supply Total supply –– losses (respiration)losses (respiration)

Supply affected bySupply affected by

PhotosynthesisPhotosynthesis

AllocationAllocation

Allocation affected by

Shoot to fruit ratioShoot to fruit ratio

Strongly affected by tree vigourStrongly affected by tree vigour

Tree vigour strongly driven by Tree vigour strongly driven by NitrogenNitrogen

Nitrogen management

Leaf analysisLeaf analysis

Fruit analysisFruit analysis

Adjust application for tree vigour Adjust application for tree vigour and yieldand yield

Remember present conditions affect Remember present conditions affect next year as wellnext year as well

IrrigationEffectively water managementEffectively water management

Water stress

Too little waterToo little water

Too much waterToo much water

Creates stress

Closes stomata and decreases photosynthesisCloses stomata and decreases photosynthesis

Decreases sugarsDecreases sugars

Possibility of fruit dropPossibility of fruit drop

Decreases Ca movementDecreases Ca movement

Changes ripening and shelf lifeChanges ripening and shelf life

Increases PPO and disordersIncreases PPO and disorders

Water stress effects

Start early in fruit developmentStart early in fruit development

Create conditions that can not be Create conditions that can not be changed laterchanged later

Fruit therefore

More likely to have postharvest More likely to have postharvest disordersdisorders

More susceptible to postharvest More susceptible to postharvest stressstress

Chilling sensitivityChilling sensitivity

During postharvest coolingFruit looses Fruit looses waterwater

Is a relationship Is a relationship between water between water loss and chilling loss and chilling injuryinjury

Effect of water loss on chilling injury

Therefore reasonable to assume

Threshold level for damageThreshold level for damage

The less water present in The less water present in exocarpexocarpat harvestat harvest

More likely to reach critical point More likely to reach critical point during coolingduring coolingHave experience from an exporterHave experience from an exporter

However

Fruit must not be too turgidFruit must not be too turgidLenticelLenticel damage increasesdamage increases

Therefore optimum irrigation Therefore optimum irrigation neededneeded

Fruit water content also affects ripening

Postharvest water loss

ABA induction

Ethylene stimulated

Ripening occurs

Water content at harvest Critical starting point

Effect of irrigation on fruit ABA ABA ng g-1 FM

Experiment to check effects of water and ABA on ripening

Effect of water and ABA on ripening

Irrigation before harvest

Modifies fruit water contentModifies fruit water content

Changes rate of ripeningChanges rate of ripening

Changes variation of ripening within Changes variation of ripening within cartoncarton

Days to ripen can be predicted by Days to ripen can be predicted by measuring water content by NIR at measuring water content by NIR at harvestharvest

How to best manage irrigation

Consider relationship between:Consider relationship between:

Soil water potentialSoil water potentialTree water potentialTree water potential

Physiological effectsPhysiological effects

StomatalStomatal closureclosureLower photosynthesisLower photosynthesis

Relationship between soil water potential and stomatal resistance

Interpretation for irrigation

To ensure no stressTo ensure no stress

Do not under or over irrigateDo not under or over irrigate

Maintain soil water potential Maintain soil water potential between 35 between 35 kPakPa and 55 and 55 kPakPa

Experience shows acceptable for Experience shows acceptable for Hass and most rootstocksHass and most rootstocks

In conclusion

Most important fertilisation Most important fertilisation driversdrivers

NitrogenNitrogen

Manage with leaf and fruit analysisManage with leaf and fruit analysisConsider yield and tree vigourConsider yield and tree vigourRemember multiple year effectsRemember multiple year effects

In conclusion

Irrigation to ensure no stressIrrigation to ensure no stress

Ensure no under or over hydrationEnsure no under or over hydration

Manage soil moisture at 35 to 55 Manage soil moisture at 35 to 55 kPakPa

Ensures good quality