Yellow Canopy Syndrome (YCS) in sugarcane is associated with altered carbon partitioning in the leaf

Understanding the metabolic and gene expression changes that accompany the expression of Yellow Canopy Syndrome (YCS) in sugarcane is important and could greatly assist in developing management strategies as well as in the identification of potential causal factors. Leaves representing two stages of development (leaves 4 and 6) from YCS symptomatic and YCS asymptomatic plants, from two seasons, were analysed using gas chromatography linked to mass spectrometry. More than 200 metabolites were detected in the leaf samples, and 84 of these could be identified. The results revealed intrinsic differences (p = 0.05) between the metabolomes of the YCS symptomatic and asymptomatic plants. It was evident that significant metabolic changes occurred well before the development of leaf yellowing. The major metabolic changes were associated with sugar metabolism, the pentose phosphate cycle, and phenylpropanoid and α-ketoglutarate metabolism. The diurnal changes of sucrose concentrations (low in the morning and high at the end of the day) are absent in the YCS symptomatic plants even before symptom expression. Comparing the leaf transcriptomes of the symptomatic and asymptomatic plants shows that a complex network of changes in gene expression underpins the observed changes in the metabolome.