Effect of the Grain Sink on Stalk Juice Yield Sugar Accumulation and Biomass of Sweet Sorghum.

Sweet Sorghums [Sorghum bicolor (L.) Moench] are among the cultivated sorghums grown for their sugar rich stalks. They are very efficient in utilizing sunlight and capturing carbon-dioxide to accumulate sugar and biomass. Since sugars are the direct results of photosynthesis, the degree to which they can be stored in the stalk depends on the strength of other sinks. The objective of this study was to determine the effect of eliminating the grain sink on juice yield and sugar accumulation in sweet sorghums. Experiments were conducted at two locations in Manhattan. Twenty-two genotypes of variable sugar and juice yield were grown in two row plots in a randomized complete block arranged in split-plots and replicated four times. Heads from each genotype from one of the rows were removed at heading and this forms the sub-plot treatments (clipped vs. unclipped) while genotypes were the main plot treatments. At physiological maturity, all plants within a pre-marked 1m section in each row were harvested and used to determine brix %, biomass, juice and sugar yield. The analysis of variance showed the effect of genotype and head removal was significant (P £ 0.01) for all traits. Elimination of the grain sink significantly increased brix % (17.29 vs. 15.09), biomass (17.14 vs. 13.39 Mg ha^-1), juice yield (13.79 vs. 10.61 Mg ha^-1), and sugar yield (1.84 vs. 1.28 Mg ha^-1). Sugar, juice yield and biomass were significantly correlated with biomass yield, stalk fresh weight and total fresh weight respectively. Genetic systems that offer opportunity to develop sterile hybrids should significantly increase the value of sweet sorghum as biofuel feedstock.