A Potassium Phosphite Solution as a Dual-Action Strategy Against Bean Anthracnose: Antifungal Activity and Defense Gene Priming

Anthracnose in beans is an important disease caused by <i>Colletotrichum lindemuthianum</i>, which affects crop productivity and infects the plant in all growth stages, affecting the quality of the pod and grains. The most viable strategy to control this disease is using bean cultivars; however, fungal variability is a limitation. Among the strategies proposed is using phosphite-based compounds, which can act as fungicides or priming stimulators. This study aimed to evaluate the antifungal activity of a phosphite-based solution (potassium phosphite (H₃PO₃), potassium hydroxide, and potassium citrate, in a formulation of phosphorus (P₂O₅) 28% and potassium (K₂O) 26%) on <i>C. lindemuthianum</i> under in vitro conditions. In addition, its effects as a defense inducer in Sutagao bean plants was determined by changes in disease severity and the expression of <i>PR1</i>, <i>PR3</i>, <i>PR4</i>, and <i>POD</i> (defense-related genes) in plants treated with the phosphite solution before infection with the fungus. The results showed that the potassium phosphite solution had a statistically significant antifungal effect on <i>C. lindemuthianum</i>, reducing mycelial growth by 42% and germination by 48%, at a dose of 5 mL L⁻¹. Foliar application of the phosphite-based solution showed a 17% reduction in anthracnose severity associated with high expression of the <i>PR1</i>, <i>PR3</i>, <i>PR4</i>, and <i>POD</i> defense genes, which increased in plants that were subsequently infected with the pathogen, demonstrating a priming effect. In conclusion, a potassium phosphite solution can be included in a management program to control bean anthracnose.