HAVE WE REACHED PEAK CCS? By

AN INCREASE in commercial cane sugar (CCS) is up to 1.8 times more valuable than a sucrose yield increase due to improved cane yield, because increased CCS does not attract high marginal costs in harvesting, transport and milling as does increased cane yield. Despite the priority in research and development investment to increasing CCS in past decades, industry mean CCS has fluctuated between 13 and 14% over the past 15 years with no obvious trend upward or downward. In this paper we consider limits to CCS and sucrose content in sugarcane and what may be done to address these limits. The maximum CCS in commercial cane delivered to mills in Australia appears to be about 18% and, while levels of sucrose in internode tissue measured in carefully controlled glasshouse conditions is only 3% units higher, we suggest that future efforts concentrate on the gap of 4 to 5% units between the highest observed CCS levels and the industrial average. This gap arises because of genetic responses to environmental factors and age, in contrast to a bio-physical limit to sucrose content already reached, and because of extraneous matter with little or no CCS. There is an opportunity to manage crops and select varieties that have higher CCS earlier in the season, and with better response to environmental factors reducing CCS. There is some evidence suggesting high CCS genotypes may be sensitive to factors affecting stem elongation. Moderate reductions in expansive growth will reduce cane volume and weight without sacrificing photosynthesis, leading to improved CCS. Ripeners could be re-evaluated with a better understanding of ripener, water, temperature and genotype interactions possibly using controlled conditions of the glasshouse. Reasons for the apparent limited progress in breeding programs in leading to increased industry CCS are not clear, but some suggestions are made for a re-evaluation of past approaches.