Improving sucrose yield is one of the main objectives of sugarcane breeding. Splitting this complex traitinto yield components should make this task easier, as each component may be influenced in its own wayby environmental factors and by genetic background. Abiotic conditions experienced by sugarcane acrossits cropping areas differ in many respects; among them, water availability and photo-thermal conditionsparticularly affect sucrose yield formation.In this study, sucrose yield was divided into seven component traits and studied in a panel of 155 sugar-cane accessions phenotyped at two sites under contrasting photo-thermal conditions: one in low altitudeand the other in higher altitude. The accessions were hybrids developed during the last century and rep-resenting the worldwide cultivated genetic diversity. The proportion of Saccharum spontaneum genomein the genome of each accession was estimated by analyzing the genetic structure of the panel associ-ated with two outgroups formed by 19 S. spontaneum and 29 S. officinarum accessions genotyped with419 DArT markers and using a Bayesian clustering method implemented in STRUCTURE software. A K = 2number of clusters clearly separated S. spontaneum from S. officinarum, while the estimated proportionsof the S. spontaneum genome in the genome of hybrid accessions ranged from 0.5 to 0.Multivariate mixed model of log transformed yield components was adjusted to estimate each com-ponent's contribution to sucrose yield genetic variance, taking into account interrelationships amongcomponents. Each component's contribution to sucrose yield variance was site-dependent. On the lowaltitude site with high photo-thermal conditions, stalk section was the main contributor to yield variance,while on the high altitude site with low photo-thermal conditions, stalk height was the main contribu-tor. A linear regression showed that the estimated proportion of S. spontaneum genome in the hybrids'genome had significant effects on sucrose yie