| Abstract | Yellow canopy syndrome (YCS) is a physiological disorder expressing as yellowing of the mid-canopy. Rapid growth following a stress period where growth rate of the top internodes has been compromised creates a supply demand imbalance. This results in high sucrose accumulation in the leaf which triggers yellowing. Accumulation of sucrose past an upper tolerance level causes partial stomatal closure, overheating, disruption to photosynthetic machinery, chloroplast destruction and leaf yellowing. Gene expression, protein and metabolite data all support a disruption to leaf metabolism as well as a strong association with abiotic stress. The data collectively shows that the metabolism of YCS-affected plants is compromised throughout the mid-canopy and occurs well before the onset of visual yellowing. Repartitioning of carbon to starch and other pools is an attempt to lessen the sucrose load within the source leaf, while also reducing oxidative stress. High levels of starch accumulation in the midrib veins of YCS leaves can be easily stained and viewed. This method can be used to reduce misdiagnosis when coaligned with correct symptom development and expression. There is no CCS penalty association with YCS, and crops can grow out of a YCS event. Management options to mitigate YCS involve best practice farming to reduce stress on the crop prior to and during the peak growing season. This will increase the sink capacity in the stalk and prevent a supply and demand imbalance. The data does not support a single cause and may therefore be either biotic, abiotic, or a combination of both. |
