Effect of White and Blue Wind Net Shading on the Quality of ‘Fuji’ and ‘Hongro’ Apple Fruits

Research Article
Article Information

  • Title: 백색 및 청색 방풍망 차광 처리가 ‘후지’, ‘홍로’ 사과 과실의 품질에 미치는 영향
  • Authors: 강경진, 서정학, 윤홍기,  서정석, 주정일, 천종필
  • Published: April 2020
  • Journal: Protected Horticulture and Plant Factory
    • Volume: 29
    • Issue: 2
    • Pages: 120-129
  • DOI: https://doi.org/10.12791/KSBEC.2020.29.2.120

Research Background


A. Research Context


  • Apple cultivation in Yesan-gun, a major apple-producing region in Korea, has been declining in both area and yield.
  • Recent climate change has led to unusually high temperatures, negatively impacting fruit quality, particularly in flatland orchards.
  • High temperatures during fruit growth stages cause issues such as poor coloration, delayed harvest, and reduced storage potential.

B. Knowledge Gap


  • While protective measures like wind nets are used to mitigate wind and hail damage, their effectiveness in reducing heat stress and improving fruit quality under high-temperature conditions remains underexplored.
  • Limited studies compare the impact of differently colored wind nets (e.g., white vs. blue) on apple fruit quality, particularly for cultivars like ‘Fuji’ and ‘Hongro’.

C. Research Objectives


  • Investigate how white and blue wind nets affect fruit surface temperature, sunburn incidence, and quality parameters (e.g., color, sugar content) in ‘Fuji’ and ‘Hongro’ apples.
  • Evaluate the nets’ ability to block UV radiation and moderate microclimatic conditions in orchards.

D. Significance


  • Provides practical solutions for apple growers to combat climate-induced heat stress.
  • Enhances marketability by improving fruit coloration and reducing sunburn damage.
  • Contributes to sustainable orchard management strategies under changing climatic conditions.

E. Additional Context


  • Previous studies highlight that temperatures above 30°C reduce photosynthesis and anthocyanin synthesis, critical for apple coloration.
  • UV radiation and excessive sunlight are key factors in sunburn, which lowers fruit quality and economic value.
  • This study builds on earlier work but focuses on color-specific wind nets as a novel approach to microclimate modification.

Materials and Methods


Experimental Setup


  • Study Location: Conducted in an apple orchard at the Chungnam Agricultural Research & Extension Service, Yesan, Korea.
  • Plant Material: 17-year-old ‘Fuji/M.9’ and ‘Hongro/M.9’ apple trees, planted in a north-south orientation with spacing of 1.5 m × 3.5 m.
  • Wind Net Treatments:
    • Installed white and blue wind nets (mesh size: 2 × 2 mm, thickness: 5 mm) at 4.5 m height above the canopy.
    • Nets were secured with galvanized steel wires and UV-resistant clips to withstand weather stress.
    • Control: Untreated trees exposed to natural conditions.

Environmental and Fruit Measurements


  • Temperature Monitoring:
    • Fruit surface and ambient temperatures recorded at 2 PM using thermocouple sensors (T-type) connected to a data logger (CR3000, Campbell, USA).
    • Thermal imaging (E8 infrared camera) used to visualize temperature differences.
  • Light and UV Measurements:
    • Photosynthetically active radiation (PAR) and UV intensity measured with a photoradiometer (Delta-OHM, Italy).
    • SPAD meter (Minolta, Japan) used to assess leaf chlorophyll content.
  • Photosynthesis Analysis:
    • Chlorophyll fluorescence imaging (Handy FluorCam) quantified photosynthetic efficiency (Fv/Fm ratio).

Fruit Quality Assessment


  • Color Parameters: Measured with a colorimeter (CR-400, Konica Minolta) for L* (lightness), a* (redness), and b* (yellowness).
  • Physicochemical Traits:
    • Fruit weight, size (length/diameter), and firmness (texture analyzer).
    • Soluble solids content (°Brix) and titratable acidity (potentiometric titration).
  • Sunburn Incidence: Visually scored as the percentage of fruit with sunburn damage at harvest.

Statistical Analysis


  • Data analyzed using CoStat software (v6.311) with Duncan’s Multiple Range Test (DMRT) at 95% confidence.

Key Notes on Methodology


  • Timing: Nets installed on June 20 and removed at harvest (‘Hongro’: August 26; ‘Fuji’: September 5).
  • Replication: Three replicates per treatment in a completely randomized design.
  • Focus: Compared microclimate modulation (temperature, UV) and its downstream effects on fruit quality.

Results & Discussions


1. Temperature Reduction by Wind Nets


  • Both white and blue wind nets significantly lowered fruit surface temperatures compared to the control.
  • At 2 PM, ‘Fuji’ apples:
    • Control: 40.0°C
    • Blue net: 34.9°C (↓5.1°C)
    • White net: 36.6°C (↓3.4°C)
  • ‘Hongro’ apples:
    • Control: 44.2°C
    • Blue net: 38.3°C (↓5.9°C)
    • White net: 38.5°C (↓5.7°C)
  • Thermal imaging confirmed blue nets were most effective in cooling.

2. UV Blocking and Light Modulation


  • Blue nets reduced UV radiation by 44% (24.9 μW/cm² vs. control: 44.6 μW/cm²), while white nets reduced it by 16% (37.5 μW/cm²).
  • Light intensity: Blue nets reduced canopy-level PAR by 18–41% compared to control, with minimal impact on photosynthesis.

3. Fruit Color Improvement


  • ‘Fuji’ apples:
    • Redness (a* value) increased by 9% (blue net) and 17% (white net) vs. control.
  • ‘Hongro’ apples:
    • White nets boosted redness by 24% (a* = 34.9 vs. control: 28.1).
  • No significant changes in yellowness (b) or lightness (L).

4. Sunburn Damage Reduction


  • ‘Fuji’: Sunburn incidence dropped from 9.4% (control) to 3.8% (blue net) and 4.2% (white net).
  • ‘Hongro’: More pronounced effect—blue nets reduced sunburn from 28.8% to 8.8%.

5. Quality Parameters


  • Soluble solids (°Brix): Increased under nets (‘Fuji’: 13.6 vs. control: 11.4).
  • Firmness and acidity: No significant differences among treatments.

6. Discussion Points


  • Temperature and UV Synergy: Blue nets’ superior cooling aligns with their higher UV blockage, mitigating thermal and oxidative stress. This explains their stronger sunburn protection.
  • Color Enhancement: White nets’ better redness in ‘Hongro’ may reflect broader light scattering, promoting anthocyanin synthesis without excessive heat.
  • Photosynthetic Efficiency: Despite light reduction, chlorophyll fluorescence (Fv/Fm ≈ 0.82–0.84) confirmed nets did not hinder photosynthesis, likely due to diffuse light benefits.
  • Practical Implications: Blue nets are optimal for sunburn-prone cultivars (e.g., ‘Hongro’), while white nets may suit color-sensitive varieties.

Conclusion


1. Climate Resilience


Both white and blue wind nets effectively mitigated high-temperature stress in apple orchards, reducing fruit surface temperatures by 3–6°C and significantly lowering sunburn incidence.

2. Color Enhancement


White nets improved fruit redness (a* value) more prominently in ‘Hongro’, while blue nets offered superior UV protection, making them ideal for sunburn-prone conditions.

3. Quality Preservation


Nets maintained or improved key quality metrics (e.g., soluble solids, firmness) without compromising photosynthetic efficiency, confirming their agronomic viability.

4. Practical Recommendation:


  • Blue nets are optimal for orchards facing extreme heat/UV exposure (e.g., ‘Hongro’).
  • White nets better enhance coloration in cultivars where visual appeal is critical (e.g., ‘Fuji’).

5. Final Statement


This study demonstrates that colored wind nets are a scalable, low-tech solution to combat climate-driven quality losses in apples, offering growers a tool to stabilize yields and marketability under rising temperatures. Future research could explore net durability and cost-benefit analysis for broader adoption.