Photosynthetic response and water relations of drought-stressed sorghum under deficit irrigation

Abstract:

Sorghum can survive drought better than most cereals, yet the physiological cost of that survival in terms of lost photosynthetic capacity and grain yield remains poorly quantified under managed deficit irrigation. This research measured photosynthetic rate, stomatal conductance, leaf water potential, relative water content, and proline accumulation in three sorghum genotypes (CSV 20, CSV 27, and SPV 2217) subjected to three irrigation regimes — 100%, 75%, and 50% of crop evapotranspiration (ETc) — at Vikram Dev Agricultural College, Jeypore, Odisha, during Kharif 2021. Severe deficit (50% ETc) reduced net photosynthesis by 47-54% and stomatal conductance by 62-71% compared with full irrigation. Leaf water potential dropped to −1.83 MPa in the most affected treatment. CSV 27 maintained the highest relative water content (68.4%) and proline levels (14.7 µmol/g FW) under severe stress, suggesting stronger osmotic adjustment. Grain yield declined 31-43% under 50% ETc, with CSV 27 recording the smallest loss. These results show that genotypic variation in water-relation traits can be exploited to select sorghum lines that sustain reasonable productivity under limited water supply.