SPAD Meter Versus Tristimulus Colorimeter to Estimate Chlorophyll Content and Leaf Color in Sweet Pepper

Abstract

The chlorophyll content and leaf color were estimated in leaves of sweet pepper by using the SPAD‐502 chlorophyll meter and the Minolta tristimulus colorimeter. In situ SPAD readings and extractable chlorophyll content were highly correlated, both for chlorophyll a (r² = 0.93) and total chlorophyll (r² = 0.89). Light reflectance (400–700 nm) measured with the tristimulus colorimeter was compared with light transmittance (at 650 and 940 nm) measured with the SPAD‐502 meter. Strong linear relationships (r² ≥ 0.93) were found between L^* (lightness) and b^* (yellow color) and the SPAD chlorophyll readings. However, a more correct form to measure leaf color is obtained from the calculation of the saturation chroma C^* and the hue angle H°. Linear and quadratic regression models were obtained between C^* and H°, and SPAD readings (r² = 0.95 and r² = 0.90, respectively), suggesting that both instruments may be used to estimate either chlorophyll content or leaf color.

Keywords:

• Leaf color
• Chlorophyll
• SPAD meter
• Tristimulus colorimeter

Acknowledgments

The work carried out by Armando Ferreira and Maria Isabel Vieira was funded by the PIDDAC Project no. 138/01 and by the Fundação para a Ciência e Tecnologia (PhD scholarship BD/21387/99), respectively. Ana Carla Madeira and Amarilis de Varennes were funded in part by the Pluriannual grant of Fundação para a Ciência e Tecnologia.