Water deficit tolerance in sugarcane is dependent on the accumulation of sugar in the leaf

Sugarcane productivity is severely affected by the occurrence of water deficit in the field, causing inhibition of growth and sugar production. Evaluating physiological responses of sugarcane under water deficit conditions is essential to understand physiological variables responsible for reaching homeostasis. Therefore, we analysed physiological traits of two sugarcane genotypes, RB835486 (Tolerant) and RB855453 (Susceptible), under water deficit conditions: well‐watered (WW‐Control), water deficit (WD) and rewatered (RW). The physiological response was evaluated using linear regression and multivariate analysis. Some characteristics such as water potential in leaves, photosynthesis, chlorophyll fluorescence, chlorophyll index, sucrose and starch contents did not show differences between the genotypes under water deficit conditions. However, the tolerant genotype showed increased reducing sugars content in the leaves, whereas the susceptible genotype had increased non‐photochemical quenching (qN). After rewatering, the susceptible sugarcane genotype showed higher electron transport rate (ETR) and efficiency of PSII (Y). Multivariate analysis revealed that non‐photochemical quenching and reducing sugars in the leaves were physiological variables responsible for reaching homestasis under water deficit conditions. Therefore, the reducing sugars concentration should be considered a physiological variable responsible for the adjustment made by the tolerant sugarcane genotype when submitted to water deficit. Principal components analysis based on physiologic variables measured on sugarcane genotypes (RB835486, RB855453) under different water conditions: well‐watered (WW, control), water deficit (WD) and rewatered (RW). Physiological traits evaluated (n = 18): water potential pre‐dawn (Wp); chlorophyll index (Chlorophyll); CO2 assimilation (A); respiration (Rd); starch; sucrose; reducing sugars (RS); yield photochemistry (Y); photochemical quenching (qP); non‐photochemical quenching (qN). Small closed circles represent individual pots and large circles represent means of scores in the two dimensions.