Optimizing Carbon Partitioning in Sweet Sorghum: A GGE Biplot and Multivariate Assessment of Biomass–Sugar Trade-Offs and Bioethanol Stability Across Water Regimes

This study investigates the physiological trade-off between biomass yield and sugar concentration in five sweet sorghum genotypes to evaluate how carbon partitioning influences bioethanol potential. Field experiments were conducted over the 2019–2020 seasons in the East Marmara transitional zone of Türkiye, under irrigated and rain-fed regimes. Results revealed a highly significant genotype × water regime interaction ( p < 0.001). A distinct trade-off was identified: while the hybrid ‘Teide’ maximized juice volume under irrigation (2427.67 L ha −1 ), ‘Leoti’ maintained superior sugar stability (18.38 °Brix) under moisture deficit. Genotype plus Genotype × Environment Interaction (GGE) biplot analysis indicated that ‘Early Sumac’ provided the highest environmental buffering, balancing productivity and sugar density across water regimes. Principal Component Analysis (PCA) demonstrated that plant height (averaging 214.2 cm) was positively associated with juice yield and concentration. Under irrigation, ‘Teide’ produced the highest bioethanol yield (1690.7 L ha −1 ), whereas ‘Nutrihang’ led output under rain-fed conditions. While these site-specific trends offer valuable insights into local bioenergy stability, further multi-location trials are necessary to confirm these patterns on a broader scale. The findings conclude that feedstock selection must be categorized by water availability to optimize sweet sorghum-based bioenergy systems in water-limited environments.