EFFECT OF GROWTH TEMPERATURE ON THE SPECTROCOLORIMETRIC CHARACTERISTICS OF SORGHUM PLANTS (SORGHUM-BICOLOR (L) MOENCH) - INDEXES 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 poss ibility of detecting the degree of alteration in sorghum leaf characte ristics by indices of stress calculated from remotely sensed data. Ref lectance, colorimetric and ecophysiological measurements were performe d 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 efficien cy in the leaves, which were less at 15 than at 32 degrees C. Slight d ifferences in these responses to temperature were also observed betwee n cultivars. Among the indices calculated, NDVI and RVI were able to d etect not only the changes caused by the growth temperature but also t he different responses of the two cultivars at the same temperature. C olorimetric coefficients detected a significant discolouration at 32 d egrees C and a marked reddening at 15 degrees C. The indices calculate d from the colorimetric data (CAI and D(X(i)-X(j))) were able to disti nguish the differences between treatments, but they did not show a str ict relationship with the trend of ecophysiological parameters.