Effect of Genotype and Genotype × Nitrogen Rate Interactions on Color in Juice and Raw Sugar from Sugarcane

There is an increased emphasis being placed on raw sugar quality in international sugar markets. Color intensity of raw sugar is one quality parameter of importance, with high color levels increasing refining costs and hence lowering sugar value. The quality of raw sugar is compromised by colored solutes or precursors of colored compounds. We examined genetic effects on color levels in juice from sugarcane (Saccharum spp.) in three field experiments, two of which also included different N fertilizer rate treatments. The relative impact on amino N in juice, an important precursor of colored compounds, was also examined. A key finding was consistently large variation among varieties (approximately threefold differences) for color and color-to-impurity ratio levels. These effects were highly repeatable across different environments and N rates, with genotype × environment and genotype x N rate interaction variance being not significant or less than 15% of genotype main effects in all experiments. Relatively small genetic effects were detected for amino N levels and these were less repeatable across environments than for color. Thus, selection for low color levels will be effective in sugarcane breeding programs. A relative color index is proposed to compare genotypes for propensity to produce color in raw sugar, considering the effects of both color and amino N in juice.