Effect of Morphological Traits Over Spectral Reflectance Indices in Spring Wheat.

Diverse morphological traits (leaf and spike orientation, awns on spikes, and wax content on leaves and spikes) were studied in spring wheat genotypes to determine their influence on the different spectral reflectance indices (SRI) and in the relationship between the SRI and grain yield under well irrigated conditions. Twenty advanced lines with contrasting morphological differences on leaves and spikes developed by the International Maize and Wheat Improvement Center (CIMMYT) were used. All genotypes were planted at CIMMYT’s experiment station in Northwest, Mexico during two growing seasons (2007, and 2008). Three vegetative indices (red normalized difference vegetative index, green NDVI, and simple ratio; RNDVI, GNDVI and SR, respectively) and five water indices (water index and four normalized water indices; WI, NWI-1, NWI-2, NWI-3, and NWI-4) were determined at heading, and grain filling using a field portable spectrometer (Analytical Spectral Devices, Boulder, CO). Considering individual effects, the spike wax content showed the major influence over the vegetative indices (9-15%), while awns on spikes were the morphological trait with the major effects (10-13%) over the water indices. For grain yield, the awns on spikes showed a significant influence (17%). When the relationship between the SRI and grain yield was tested adjusting and non-adjusting their values using the morphological traits as covariables, the correlations values were altered. Spike orientation and the presence of awns on spikes decreased the relationship between SRI and grain yield. For leaf orientation, the relationship (SR-grain yield) was decreased the for the water indices, but increased for the vegetative indices.