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SUNSCALD OF FRUIT

SUNSCALD OF FRUIT. Preston K. Andrews Department of Horticulture & Landscape Architecture Washington State University. HISTORY. First referred to as sunscald of beans by McMillan in 1918 Sunscald of apples described by Knight in 1922

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SUNSCALD OF FRUIT

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  1. SUNSCALD OF FRUIT Preston K. Andrews Department of Horticulture & Landscape Architecture Washington State University

  2. HISTORY • First referred to as sunscald of beans by McMillan in 1918 • Sunscald of apples described by Knight in 1922 • “Exposure to sunlight …most important determining factor” (Brooks & Fisher 1926) • Shade fruits with foliage or artificial covers (Moore & Rogers 1943)

  3. SUNSCALD • All injuries to plant tissues resulting from exposure to sunlight (Walker 1952, 1957) • Types (Barber & Sharpe 1981): • Heat injury sunscald • Ultra-violet radiation sunscald • Photodynamic sunscald of heated tissues

  4. SUNSCALD • Heat injury: absorption of infrared radiation  cooked appearance • Ultra-violet sunscald: common on fruits at high altitudes • Photodynamic sunscald: absorption of visible light energy by photosensitive pigmented cells with temperature-induced chemical lesions

  5. SYMPTOMS • Discoloration: silvering, yellowing, browning or blackening (apple, tomato, pepper) • Surface droplets (squash) • Water-soaked blisters (tomato, pepper)

  6. SUSCEPTIBILITY FACTORS • Solar absorptivity • Infrared radiation - surface color • Visible radiation - pigments • Interception of solar radiation • Shading by foliage • Transpirational & convective properties • Acclimation • Light & lower soil moisture • Temperature tolerance

  7. SUSCEPTIBILITY FACTORS • UV tolerance • Mature fruit more susceptible than green fruit (pigmentation) • Pigment photostability • Chlorophyll-caroteniod complex • Green tissue: impair of photoprotection by carotenoids  photooxidation products • Red tissue: presence or absence of Chl (“muddy” appearance)

  8. FRUIT MATURITY Tomato, 30-hr exposure Retig & Kedar, Israel J Agric Res 17:77, 1967

  9. Rabinowitch et al, Scientia Hortic 19:9, 1983

  10. ENERGY BUDGET EXPT • Sweet pepper (Capsicum annuum) • ‘California Wonder’ - dark green, pendant fruit • ‘College Gold’ - ivory-yellow, erect fruit • Sunscald frequency (40oC air temp) • Cal Wonder = 100%, ‘College Gold’ = 8% • Sunscald initiation • Cal Wonder - surface 49oC for 15 min in full sun • College Gold - max surface 41oC (no sunscald) Barber & Sharpe, Agric Meteor 8:175, 1971

  11. ENERGY BUDGET • Assumptions: • Heat production from respiration negligible • Light transmission through fruit small • Absorbed energy stored in organic compounds & emitted fluorescence negligible • Dissipation of radiant energy • Reflected radiation • Emitted long-wave radiation • Convective & conductive heat loss • Latent heat of vaporization

  12. ENERGY BUDGET

  13. Ivory Green

  14. RADIANT HEATING I(1-)cos  = k(T/r) + hT Energy absorbed = heat influx – heat loss I = irradiance  = reflectivity of surface  = incident angle of irradiance (where cos  is + only) k = thermal conductivity T = temperaturesurface – air r = radius h = heat loss (radiative, convective, latent)

  15. Thorpe, J Appl Ecol 11:755, 1974

  16. SUNSCALD TOLERANCE • Tomato fruit, ‘Rehovot 13’ • Fruit exposure: • Sun-exposed • Shaded • Bagged (black) from 7 after anthesis • Mature green fruit insolated for 1 day Retig et al, Scientia Hortic 2:29, 1974

  17. SUNSCALD TOLERANCE

  18. SUNSCALD INDUCTION • Mature green tomato & sweet pepper • Treatment stages: • Induction: 12-18 hr at 45-46oC • Incubation: 60 hr at 25oC • Light treatment: • 32% full sunlight applied with fluorescent + incandescent lamps • + or – during induction & incubation stages Rabinowitch et al, Scientia Hortic 2:265, 1974 & 29:21, 1986

  19. SUNSCALD INDUCTION Sunscald (%) Induction – – + + Incubation – + – + Light

  20. Rabinowitch et al, Scientia Hortic 2:265, 1974

  21. SUNSCALD ACCLIMATION • Mature green tomato (‘Moneymaker’) • Acclimated in 2 steps: 1. Induction: pericarp reaches 45oC after 6 hr 2. Rest (potentiation): 23-27oC for 15 hr • Mature green sweet pepper (‘Maor’) • Acclimated by insolation in black bags up to 5 days Kedar et al & Rabinowitch et al, Scientia Hortic 3:83, 1975 & 29:21, 1986

  22. Sweet pepper

  23. HYPOTHESES • Acclimation • Insolation (light intensity & duration) • Rest (chilling temp?) • Sunscald damage • Stage of development (chlorophyll degradation) • High temperature & light • Photodynamic injury • Photosynthetic inhibition • Chlorophyll photosensitized • O2 + visible light  photooxidation

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