Improving biomass production and partitioning in sugarcane: theory and practice

Abstract

Sucrose yields in sugarcane ( Saccharum spp.) could be improved by increasing the efficiency of biomass production per unit of intercepted radiation and/or by increasing the fraction of total biomass partitioned to stalk sucrose, or both. In theory, this could be achieved by optimally matching the physiology of genotypes to the driving environmental conditions. Quantitative knowledge of the subtle effects of climate and genotype is therefore required to optimise cultivar choice, time of harvest, irrigation and chemical ripening. The objective of this paper is to review existing knowledge of the effect of time of harvest and cultivar on the assimilation and partitioning of biomass in sugarcane by comparing modelling theory and published literature with observations from selected experiments conducted at Pongola, South Africa. Simulations were compared with observations for well-watered crops harvested at different times of the year at Pongola, South Africa. Crops started in April and May seem to have higher radiation use efficiencies than other crops, thereby compensating for lower interception of radiation during this time of the year. Winter-harvested crops partitioned a smaller fraction of final biomass to leaves and more to stalks than summer-harvested crops. This trend was not simulated by the Canegro model. Simulations were partially improved by refining the model to account for temperature control of photosynthesis and respiration. The observed seasonal peak of stalk sucrose content also occurred later than simulated, while the observed decrease in sucrose content from January to April could not be reproduced by the model. These shortcomings have serious implications for the relevance of the model as a tool for identifying crop improvement and management strategies. However, the Canegro model successfully mimicked partitioning of assimilate to stored sucrose using two cultivar parameters. Results suggest that there is scope for improving yields but that the optimisation process should include all components of the sucrose production process in sugarcane, including radiation capture, net photosynthetic efficiency and stalk partitioning. Sufficient understanding of the interactions between these components is lacking. There is a need for models to distinguish between photosynthesis and respiration and the strong dependence of both on temperature should be taken into account. Sinks for leaf, stalk structure and sucrose need to be considered separately to adequately understand the effect of temperature on partitioning.