Beneficial Spectral Characteristics of Red and Black Raspberry Plants (Rubus idaeus and Rubus occidentalis)

ABSTRACT

Raspberry naturally occurs in association with trees as a forest border species, thus is ideally adapted for species-diverse agroforestry systems. In spite of thriving in relatively low solar radiation environments, some red (European) and black (North American) raspberry (Rubus idaeus L. and Rubus occidentalis L.) plant surfaces are highly reflective, both species on leaf abaxial surfaces and black raspberry on cane surfaces. Cane surface color varies from green to red. The objective of this study was to quantify plant spectral characteristics in order to assess their potential ecological significance. Leaf reflectance and transmittance were determined using a spectroradiometer with integrating sphere and regulated light source. Reflected irradiance from leaves and canes was measured under natural sunlight with a microscopic lense attachment. Reflectance of abaxial leaf surfaces was 4.3 and 5.3 times greater than abaxial leaf surfaces for red and black raspberry, respectively. This amounted to 27 and 29% of possible reflectance for red and black raspberry compared to a white standard. The glaucus coating on black raspberry canes reflected nearly 50% as much as a white standard. The red color of cane surfaces was due to higher absorption of green and yellow wavelengths rather than increased red reflection. The variety of spectral strategies employed suggest a sophisticated system of protection from pests, disease, herbivores, ultraviolet radiation, oxygen free radicals, and extreme moisture conditions.

KEYWORDS:

• Agroforestry
• glaucous
• hydrophobic
• reflectance
• pubescence