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Foliar application of manganese increases sugarcane resistance to orange rust

Orange rust (Puccinia kuehnii) is a serious disease compromising the sustainability of sugarcane (Saccharumspp.) pro-duction. The objective of this research was to study whether supplemental manganese (Mn) supplied through foliarsprays ameliorates negative effects of orange rust on sugarcane and, if so, to reveal the underlying mechanisms. Theexperiment was conducted using a sugarcane variety susceptible to the disease; a single spray of Mn at 5 g L1 (Mn0.5%) or10gL1 (Mn1%), plus a control (Mn0%) was performed before pathogen inoculation. Symptom severity,antioxidant metabolism, lignin deposition and anatomical organization were evaluated. Photosynthesis was also mea-sured in newly expanded leaves and plants were harvested to estimate growth responses. The percentage diseased leaf area was reduced from 15% under Mn0% to 2.2% and 0.9% under Mn0.5% and Mn1%, respectively. This decreasewas accompanied by increases in biomass production in the plants. Scanning and light microscopy images revealed thatMn treatment caused direct damage to the fungal spores and improved lignin deposition in the mesophyll. In the pres-ence of the disease, Mn-sprayed leaves exhibited lower levels of oxidative stress, in addition to improved structuralorganization of xylem and phloem vessels compared to the untreated control. The negative effects of orange rust on gas exchange and photochemistry were also ameliorated by Mn application. The results give insight into the mecha-nisms underlying augmented sugarcane resistance to orange rust under supplementary foliar Mn spray and contribute to the development of sustainable crop production systems by offering alternatives for reduction of disease damage.

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