Leaf thickness and gas exchange are indicators of drought stress tolerance of sugarcane
The frequent occurrence of prolonged droughts has become a very negative factor in the sugarcane crop production worldwide. Ratoon sugarcane, after second crop cycle, can response to drought stress is different as first crop cycle. Thus, this study aimed to investigate the biometric and physiological responses of sugarcane varieties under drought stress conditions of ratoon crop sugarcane. Our hypothesis is that some biometric and physiological characteristics of sugarcane are correlated with its drought tolerance. Six sugarcane varieties were used: 1-RB72910, 2-RB99382, 3-RB72454, 4-RB92579, 5-RB855536 and 6-RB931011, and three water treatments based on soil available water content (SAWC) and defined as: 1-control, 80 to 100% SAWC; 2-moderate water stress, 40 to 60% SAWC and 3-severe water stress, 0 to 20% SAWC. The RB92579 variety was the most tolerant to drought, with less alteration in its biometric and physiological characteristics under drought stress. On the other hand, RB72454 variety was the most affected by drought stress, with high reduction in gas exchange and plant growth. Sugarcane leaf width, specific leaf area, stomatal conductance, transpiration, photosynthesis and carboxylation efficiency were quite sensitive to changes in soil moisture and can be used by breeding programs to discriminate sugarcane varieties more tolerant to drought stress.