Combined effect of yeast and silicon on the control of bacterial fruit blotch in melon

• Silicon and yeasts separated or combined reduced the severity of bacterial fruit blotch in melon.
• No additive or synergistic effects of the yeasts/Si combined treatments were observed.
• The durability of protection in melon plants with LMA1 and/or Si was 29 days.
• Increases in the enzymatic activity by LMA1 and/or Si may be related to resistance induction.

The combined effect of the antagonistic yeasts Rhodotorula aurantiaca LMA1, Rodothorula glutinis LMS and Pichia anomala CC-2 and silicon (Si) was evaluated in relation to the control of bacterial fruit blotch (BFB) caused by Acidovorax citrulli in seedlings and plants, and possible mechanisms of action involved in the control were analyzed. The incorporation of 1.41 g Si kg−1 (calcium silicate) into the substrate, together with foliar spraying with yeast (1.5 × 107 cells mL−1) and foliar spraying with 17 mM Si (potassium silicate) and the yeasts, separately or in combination, reduced the severity of the disease and protected seedlings and plants. These plants were inoculated with A. citrulli by foliar spraying (3.4 × 107 UFC mL−1) 24 h following the treatment. However, no additive or synergistic effects of the combined treatments were observed. The spraying of LMA1 + Si and LMA1 resulted in the highest levels of control of BFB in plants, and this level of control was higher than that provided by acibenzolar-S-methyl. Foliar spraying with LMA1 and Si, either separately or in combination, protected melon plants from infection by A. citrulli for 29 days. Increases in the activity of polyphenol oxidase after foliar spraying with Si and LMA1, and increases of ascorbate peroxidase activity after foliar spraying with LMA1 + Si and LMA1 are likely related to the induction of resistance to BFB.