Response of Photosynthetic and Root Traits of Sugarcane Genotypes Under Drought and Recovery Conditions

The aim of this study is to investigate physiological responses and root characteristics of four sugarcane genotypes under drought stress and recovery conditions. The experiment was conducted in rhizoboxes under greenhouse conditions from February to May of 2019. A factorial experiment in completely randomized design with two replications was employed. Factor A contained three water regimes (full irrigation, drought, and recovery) and factor B consisted of the four sugarcane genotypes; Biotec 1, PR3067, UT6, and UT12. Data were recorded on physiological parameters, root characteristics and biomass yield. Early-drought led to a reduction in the relative water content (RWC), SPAD chlorophyll meter reading (SCMR), chlorophyll fluorescence (Fv/Fm), stomatal conductance (gs), transpiration rate (E), net photosynthetic rate (Pn), root length (RL), root surface area (RSA), root diameter (RD), root volume (RV), and biomass. Conversely, water use efficiency (WUE) increased. Biotec 1 showed low reductions on Fv/Fm, SCMR, Pn, gs and E whereas PR3067 and UT 12 showed high reductions for all traits. After rewatering, four parameters (SCMR, Fv/Fm, Pn, and WUE) illustrated how the sugarcane genotypes recovered from drought. We concluded that the ability of sugarcane to recover from drought was genotype dependent. Genotype Biotec 1 and UT 6 had the best drought recovery among the other sugarcane genotypes in each parameter and recover to levels equal to that of full recovery. Genotype Biotec 1 showed good recovery for SCMR, Fv/Fm and RL but Pn and WUE cannot reach to the full irrigation. Interestingly, UT 6 displayed good recovery for SCMR, Fv/Fm, Pn, RL and WUE. Additionally, the Biotec 1 and UT 6 genotypes demonstrated a high recovery efficiency for biomass by 85% and 79%, respectively. Despite rewatering, genotypes PR3067 and UT 12 produced low recovery efficiency at 56% and 49%, respectively. Our study proposes Biotec 1 and UT 6 as drought-tolerant genotypes capable of maintaining satisfactory photosynthetic rates, as well as suitable root systems, leading to high biomass after recovery. Furthermore, breeders can utilize this genotype as a parent in sugarcane breeding for drought resistance, and photosynthetic and root traits could be used as selection criteria for enhancing sugarcane drought resistance.