Gas exchange and chlorophyll a fluorescence of sugarcane varieties submitted to water stress

Water stress affects a great part of the world's agriculture. Thus, this work was conducted to evaluate photosynthetic traits in four varieties of sugarcane (SP79-1011, RB72454, RB98710 and RB92579) submitted to water stress during the early stage of the vegetative period. The plants were cultivated in plastic pots (15 kg of soil). The study was a factorial (4 varieties x 3 levels of soil water content based on available water capacity (AWC)), in a completely randomized design with 5 replications. The levels of water content in the soil were as follows: control (80 to 100% of AWC), moderate water stress (40 to 60% of AWC) and severe water stress (0 to 20% of AWC). Water stress provoked a significant reduction in stomatic condutance (g(s)), foliar transpiration (E), net photosynthesis (A) and in the water use efficiency of production (WUEy), irrespective of varieties. The varieties SP79-1011 and RB98710 showed greater stomatal sensitivity, reducing gs and E by the 71 days after the beginning of the water stress treatments, even in the control. However, under such conditions A was little affected, indicating that the plants are capable to fixing CO2 with stomata partially closed. Water stress caused a small reduction in the potential photochemical efficiency (F-v/F-m ratio) in the studied varieties.