Assessment of Photosynthetic Pigment and Water Contents in Intact Sunflower Plants from Spectral Indices

Under water-limited conditions, monitoring water and chlorophyll status is essential to avoid restrictions in crop growth and yield. This study was carried out to assess water and chlorophyll contents from spectral indices in sunflower plants. The hybrid Sunbright Supreme was cultivated inside a non-acclimatized greenhouse until the start of the flowering stage, and later was maintained in a growth chamber with the purpose of submitting the plants to a slow and progressive dehydration rate for 12 consecutive days. Spectral (reflectance and transmittance), leaf masses (fresh and dry), and total chlorophyll measurements were accomplished in sunflower plants. The water stress caused a reduction in the water and chlorophyll contents, resulting in linear and nonlinear decreases for the spectral indicators Water Index (WI) and Chlorophyll Content Index (CCI), respectively. The low scattering of the average values around the fitted models indicates that WI and CCI were effective in representing changes in water and chlorophyll status for sunflowers (R-2 = 0.912 and R-2 = 0.905). The benefits of using hand-held optical meters for reflectance and transmittance are that they enable rapid, accurate, and nondestructive assessments of water and chlorophyll contents in sunflower plants from radiometric indicators.