SPAD meter versus tristimulus colorimeter to estimate chlorophyll content and leaf color in sweet pepper

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 alpha (r(2) = 0.93) and total chlorophyll (r(2) = 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 (r(2) greater than or equal to 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 Hdegrees. Linear and quadratic regression models were obtained between C* and Hdegrees, and SPAD readings (r(2) = 0.95 and r(2) = 0.90, respectively), suggesting that both instruments may be used to estimate either chlorophyll content or leaf color.