Correlation between SPAD Values and RARSa, PSSRa, RARSb, and RARSc
The phenotypic correlations and the correlation among genotypes between chlorophyll concentration (SPAD unit) and other spectral reflectance based indices to estimate the concentration of chlorophyll and carotenoids (RARSa, PSSRa, RARSb, and RARSc) are presented in Table 7.
The SPAD and other visible wavelength based spectral indices (PSSRa, RARSb and RARSc) gave the highest values at the booting stage and maintained a similar value at the heading stage.
Even though RARSa and PSSRa are indicators of the chlorophyll-a concentration in the plant, a differential performance was observed between these indices to distinguish genotypes for biomass production.
RARSa, RARSb, and RARSc were developed to estimate chlorophyll-a, chlorophyll-b, and carotenoids in soybean (Chappelle et al., 1992), and PSSRa was developed to estimate chlorophyll-a in a range of plant species (Blackburn, 1998).
In this study, we have observed strong relationships between SPAD readings and PSSRa, RARSb, and RARSc when estimated at the heading and grainfilling stages, but the relationship was poor at booting.