Apple fruitlet physiological characteristics and their influence on diffuse visible/near-infrared reflectance...

Area of Science:

• Horticulture
• Plant Physiology
• Remote Sensing

Background:

• Digital technologies are increasingly used in agriculture.
• Understanding plant physiological characteristics is key to interpreting light reflectance data.
• Young apple fruitlets undergo rapid developmental changes affecting their spectral properties.

Purpose of the Study:

• To characterize changes in 'Fuji' and 'Honeycrisp' apple fruitlets.
• To understand how fruit size, chlorophyll, and trichome density affect diffuse spectral reflectance.
• To inform the development of digital agronomic tools.

Main Methods:

• Visible and Near-Infrared (Vis/NIR) reflectance spectra were collected from 20 to 36 days post-bloom.
• Principal Component Analysis (PCA) and vegetation indices were calculated from spectral data.
• Trichome density, water content, and chlorophyll concentration were quantified; relationships were analyzed using regression and correlation.

Main Results:

• Fruit size was the primary driver of variation in reflectance spectra (86.56% in the first principal component).
• Larger fruit size correlated with lower reflectance at chlorophyll and water absorption wavelengths.
• While chlorophyll concentration decreased with size, total chlorophyll content increased, showing a stronger relationship with size than trichome density.

Conclusions:

• Fruit size and total chlorophyll content are the dominant factors influencing apple fruitlet reflectance spectra.
• The amount of fruit tissue within the spectrometer's field of view significantly impacts measurements.
• Cultivar-specific differences in chlorophyll content may have implications for fruit photosynthetic capacity.