Real Time PCR (qRT-PCR) analysis of Populations gene expression. The y axis refers to the relative expression ratio between target mRNA versus the reference mRNA (polyubiquitin-PUB SCCCST2001G02.g). The relative expression levels were determined in Internode 1, 5 and 9 tissues from a pool of the eight individuals with the highest Brix measures (HB) and the eight individuals with the lowest Brix measures (LB) from Population 1 (A) and from a pool of the seven individuals with the highest Brix measures (HB) and the seven individuals with the lowest Brix measures (LB) from Population 2 (B). The reactions for the target mRNA and reference mRNA were carried out in parallel and each reaction was performed in triplicates. Error bars were calculated as described previously . The transcript levels for the reference genes were verified not to vary in response to the treatments. The values of P correspond to the probability Pr(HB>LB) and Pr(HB<LB) for up- and down-regulated genes, respectively. The SAS was considered differentially expressed when P ≥ 0.95.