EFFECT OF PREHARVEST FACTORS ON...
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Transcript of EFFECT OF PREHARVEST FACTORS ON...
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