To investigate the processes involved in the susceptibility of sugarcane plants to water deficit, several physiological parameters
were evaluated in drought tolerant (SP83-2847 and CTC15) and sensitive (SP86-155) cultivars. The water deficit affected the
photosynthetic apparatus of all the plants in different ways, within and among cultivars. The photosynthetic rate and stomatal
conductance decreased significantly in all cultivars submitted to water deficit. In control plants of the tolerant cultivars (SP83-2847
and CTC15) the photosynthetic rate was higher than in the sensitive cultivar (SP86-155). Cultivar CTC15 showed the highest relative
water content during the dry period. The quantum efficiency photosystem II of cultivar SP83-2847 was more stable in the last days
of the experimental treatment, suggesting that the decline in relative water content stimulated an adjustment of photosynthetic
capacity to tolerate the changes in water availability. As a whole, the tolerant SP83-2847 and CTC15 cultivars exhibited a better
photosynthetic performance than the sensitive SP86-155 cultivar. The data suggest that these physiological parameters can be used
in the evaluation and distinction of drought tolerant and sensitive sugarcane genotypes.
