Photosynthetic Nitrogen Use Efficiency and Their Contribution to Yields of Diverse Sugarcane (Saccharum Spp.) Genotypes Grown Under Early Drought Conditions

Physiological and photosynthetic nitrogen use efficiency responses to early drought and their contribution to yields in diverse sugarcane genotypes are understudied. This study examines the physiological responses, photosynthetic nitrogen use efficiency (PNUE), and their relationship with yields in various sugarcane genotypes during early drought and recovery periods, providing information relevant to breeding drought-resistant sugarcane. The experiment was arranged in a split-plot in RCBD with three replications. The main plot was two water regimes (i) well-watered (WW) and (ii) early drought stress (DS), whereas the subplot consisted of six sugarcane genotypes in plant cane and ratoon cane. Relative water content (RWC), SPAD chlorophyll matter reading (SCMR), stomatal conductance (gs), photosynthetic rate (Pn), PNUE, and crop growth rate (CGR) were measured during drought and recovery periods. While cane, sugar, and fiber yield were collected at the final harvest. The results indicated that drought stress reduced RWC, SCMR, gs, Pn, PNUE, and CGR. Furthermore, early drought reduced cane, sugar, and fiber yields, as well as CCS levels. After rewatering, RWC, Pn, gs, PNUE, and CGR quickly recovered in only F03-362 genotype. PNUE significantly contributed to CGR under DS conditions and enhanced cane yield during drought. Under DS conditions, F03-362 maintained high PNUE and GCR, while F03-362 and KK09-0358 sustained high PNUE and cane yield. Interestingly, F03-362 as an F1 hybrid showed a good recovery efficiency for Pn, PNUE, and GCR, resulting in a high cane yield. Breeders can use this genotype as a parent in sugarcane breeding for drought resistance, with PNUE and CGR serving as selection criteria. Understanding the water stress-response mechanisms of diverse genotypes is key to successful drought-resistant breeding.