2007 Annual Report 1a.Objectives (from AD-416) Using available genetic populations that have been selected for differences in sucrose concentration, identify differential gene expression and metabolism associated with differences in sucrose accumulation, and develop testable hypotheses about the molecular events that determine accumulation. Using the same selected populations as appropriate, describe the relationships between sucrose concentration in stalks and other traits that are potentially important for co-product development. Emphasis will be placed on characterizing the relationships that may contribute to suitability for conversion to ethanol. 1b.Approach (from AD-416) Using sibling progeny of a high sucrose x high biomass cross, determine differences in partitioning of sucrose between growth, cell wall biosynthesis, and storage as sucrose. Manipulate source-sink relationships in selected progeny through the application of phytohormones to determine the role of soluble acid invertase in influencing partitioning among competing processes. Determine the genetic variability in cell wall composition in stalks of basic sugarcane germplasm. Determine changes in cell wall composition of internodes during development. 4.Accomplishments Study of 35 historical varieties demonstrates that yield and juice quality improvements in sugarcane have reached a plateau in Louisiana. Growth, yield and juice quality were measured in the first ratoon crop of 35 historical varieties representing seven cycles of recurrent selection for sucrose. These included some of the oldest varieties, selected in the 1930’s, and some of the newest varieties, selected in the 1990’s. Results verified that juice quality improved with each of the first four cycles of selection, and reached a plateau in the final three cycles where cane yield was highest among the varieties of the most recent three cycles of recurrent selection. Earlier spring emergence by the newer varieties that appears to correlate with cane yield when this attribute was not specifically selected during development of historical varieties indicates that by directly selecting for early spring emergence sugarcane breeders may further increase cane yields. This accomplishment addresses NP 302 Plant Biological and Molecular Processes, Component 2. Biological Processes that Improve Crop Production and Quality. Problem Statement 2A: Understanding Growth and Development.