Combined application of Pseudomonas chlororaphis strains and zinc suppresses Alternaria alternata leaf spot in chili pepper.

Combining Pseudomonas chlororaphis strains ARS-38 and RP-4 with zinc (2 mg/kg) reduced Alternaria alternata leaf spot disease incidence by 96% in chili pepper under open-field pot conditions.

• Why it matters: Chili pepper is vulnerable to Alternaria alternata, which causes leaf spot/blight and fruit rot, and biological control is needed to reduce reliance on chemical fungicides.
• What they did: In vitro, ARS-38 and RP-4 inhibited A. alternata growth by 62% and 64%, respectively, and zinc-amended medium increased inhibition to 70% individually and 93% when combined; microscopy showed conidia and conidiophore disintegration.
• The result: In planta, A. alternata infection caused 100% disease incidence, while ARS-38 + RP-4 in Zn-amended soil increased lignin and phenolic accumulation, reduced enzyme activities, and substantially suppressed disease development.