Site and Saccharum spontaneum introgression level drive sugarcane yield component traits and their impact on sucrose yield in contrasted radiation and thermal conditions in La Réunion

Abstract

Improving sucrose yield is one of the main objectives of sugarcane breeding. Splitting this complex trait into yield components should make this task easier, as each component may be influenced in its own way by environmental factors and by genetic background. Abiotic conditions experienced by sugarcane across its cropping areas differ in many respects; among them, water availability and photo-thermal conditions particularly affect sucrose yield formation.In this study, sucrose yield was divided into seven component traits and studied in a panel of 155 sugarcane accessions phenotyped at two sites under contrasting photo-thermal conditions: one in low altitude and the other in higher altitude. The accessions were hybrids developed during the last century and representing the worldwide cultivated genetic diversity. The proportion of Saccharum spontaneum genome in the genome of each accession was estimated by analyzing the genetic structure of the panel associated with two outgroups formed by 19 S. spontaneum and 29 S. officinarum accessions genotyped with 419 DArT markers and using a Bayesian clustering method implemented in STRUCTURE software. A K=2 number of clusters clearly separated S. spontaneum from S. officinarum, while the estimated proportions of 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 component's contribution to sucrose yield genetic variance, taking into account interrelationships among components. Each component's contribution to sucrose yield variance was site-dependent. On the low altitude 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 contributor. A linear regression showed that the estimated proportion of S. spontaneum genome in the hybrids’ genome had significant effects on sucrose yield and its components. These effects also varied with the site: under low altitude conditions, the estimated proportion of S. spontaneum genome in the hybrid's genome exerted a significant negative effect on sucrose yield, whereas no significant effect was found under high altitude conditions. These results suggest that both efforts toward introgression and selection on yield components for sugarcane breeding purposes should depend on the targeted cropping environment.