Is magnesium deficiency a causal agent of sugarcane Yellow Canopy Syndrome? : ASSCT peer-reviewed paper
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Yellow Canopy Syndrome (YCS) is a disorder affecting sugarcane in the Australian industry, the cause of which is unknown. This paper reviews YCS research focusing on magnesium imbalance as a possible cause of the condition. Four studies were undertaken to evaluate the role of Mg in YCS incidence and severity. In Trial 1 sugarcane leaves were collected at multiple locations in the Burdekin and Herbert with samples taken from sugarcane blocks with both YCS symptomatic and asymptomatic plants. Despite adequate soil-Mg, leaf-Mg concentrations were significantly lower (p?0.05) in leaves 2, 3, 4, 5 and 6 of YCS symptomatic plants in both regions suggesting an imbalance of this critical nutrient. Trial 2 measured Mg concentrations in sugarcane leaves before, during, and after YCS symptom expression. Symptomatic cane showed decreased leaf-Mg concentrations, but this returned to normal levels once the cane recovered. Trial 3 treated YCS symptomatic cane with foliar and soil applications of Mg in an attempt to mitigate the condition. Neither treatment resulted in alleviation of the YCS symptoms. Trial 4 treated sugarcane with foliar-Mg and soil-Mg prior to onset of symptoms. Despite elevating the Mg concentration in leaves, these pre-symptomatic treatments did not prevent YCS expression and plants exhibited YCS symptoms similar to that of the untreated control. We conclude that YCS affected cane is associated with reduced leaf Mg concentrations, but it is unlikely that this is the cause of YCS per se, as concentrations were well above critical thresholds for plant health. YCS occurs independently of Mg and low Mg is an indirect effect rather than a cause. Given that disruption to plant nutrient balance has been described as a symptom of some plant diseases, we speculate that these findings suggest a biotic causal agent.