Effect of growth temperature on the spectrocolorimetric characteristics of sorghum plants (Sorghum bicolor (L) Moench): Indices of stress

In the leaves of herbaceous plants sub-optimal temperatures influence the content and efficiency of the photosynthetic pigments and, in more severe cases, alter mesophyll thickness. This paper examines the possibility of detecting the degree of alteration in sorghum leaf characteristics by indices of stress calculated from remotely sensed data. Reflectance, colorimetric and ecophysiological measurements were performed on two cultivars of sorghum (Sorghum bicolor (L.) Moench.) grown at 15, 21 and 32 degrees C. Compared to plants grown at 21 degrees C, the other two temperatures reduced chlorophyll content and PS II efficiency in the leaves, which were less at 15 than at 32 degrees C. Slight differences in these responses to temperature were also observed between cultivars. Among the indices calculated, NDVI and RVI were able to detect not only the changes caused by the growth temperature but also the different responses of the two cultivars at the same temperature. Colorimetric coefficients detected a significant discolouration at 32 degrees C and a marked reddening at 15 degrees C. The indices calculated from the colorimetric data (CAI and D(X(i)-X(j))) were able to distinguish the differences between treatments, but they did not show a strict relationship with the trend of ecophysiological parameters.