Impact of silicon application on downy mildew severity in melon plants during the rainy season

ABSTRACT Downy mildew is one of the main foliar diseases affecting melon plants during the rainy season in the Northeast region of Brazil. Silicon (Si) application has emerged as an alternative method for pathogen control, forming physical barriers and activating defense mechanisms in plants. The objective of this study was to reduce the severity of downy mildew in melon plants during the rainy season through foliar application of Si. The treatments consisted of five rates (0, 0.25, 0.5, 1, and 2 L ha-1) of potassium silicate (12% Si and 15% potassium) applied from May to July 2022, with four replications. Disease severity was assessed using rating scales, chlorophyll contents, and transient chlorophyll a fluorescence (OJIP). The rate of 2 L ha-1 resulted in the best results by delaying pathogen development in leaves with disease incidence. Disease severity decreased to 68.27% and chlorophyll a, b, and total increased by 8.21%, 13.86%, and 9.72%, respectively. Si application resulted in beneficial changes in the following OJIP test parameters: ABS/RC, TR0/RC, ET0/RC, ABS/CS0, and TR0/CS0. During periods of high rainfall intensity and mild temperatures, Si application to melon plants reduces downy mildew severity and protects chlorophylls, enhancing the absorption flux (ABS) and electron storage (TR0) and transport (ET0).