Recurrent Selection for Sucrose Has Altered Assimilate Partitioning Between Growth and Storage in Sugarcane Internodes.

Sucrose yield in sugarcane  (Saccharum spp. hybrids) is a function of sucrose content of the cane and cane yield. Selection for sucrose content is a high priority in sugarcane breeding programs. Louisiana sugarcane breeding programs have used a modified recurrent selection program whereby genotypes with high sucrose content are crossed to produce the next generation of seedlings from which to select new cultivars.  There have now been six cycles of recurrent selection for sucrose in the Louisiana breeding programs, resulting in seven generations of cultivars. We planted five cultivars from the foundation generation (Generation 1) and the most recent generation (Generation 7) of cultivars. We flagged 20 stalks per plot, and marked the topmost internode on each. We then sampled one of the marked internodes at one to two-week intervals for 12 weeks, and measured length, fresh weight (FW), dry weight (DW), water content, and soluble sugars. Internodes of Generation 7 cultivars were shorter than those of Generation 1 because they elongated for slightly less time. Internodes from Generation 7 cultivars had a lower FW, but the same DW as those from Generation 1. After elongation stopped, water content of the internodes started to decrease. Water content decreased faster in Generation 7 cultivars than in Generation 1.  Internodes of Generation 7 cultivars accumulated more total sugar and more sucrose, and had a higher sucrose:total sugar ratio than those of Generation 1. We conclude that recurrent selection for sucrose has altered the partitioning of assimilates between growth and storage within the internodes.