Mustard Seed Meal Volatiles Inhibit Vegetative Growth and Spore Germination In Phytophthora Capsici and Verticillium Dahliae, Two Soilborne Pathogens of Chile Pepper.

Cruciferous crop residues and byproducts including green manures and seed meals produce volatiles that have been shown to be efficacious against several soilborne plant pathogens. This study was conducted under controlled environment to examine the effects of mustard seed meal (MSM)  volatiles on mycelial growth and spore germination in Phytophthora capsici and Verticillium dahliae, two soilborne pathogens of many vegetable crops including chile pepper (Capsicum annuum). One-day-old culture of each pathogen on potato dextrose agar (PDA) in 9-cm plastic petri plates were inverted and sealed in place over petri plates containing 0, 1, or 2 g of mustard seed meal mixed with 20 ml of sterile distilled water. Similarly, PDA plates, seeded with encysted zoospores of P. capsici or conidia of V. dahliae, were exposed to MSM volatiles. All plates were maintained for 14 days for V. dahliae and 3 days for P. capsici in darkness at 20, 25, and 30^oC. Regardless of temperature, no mycelial growth was recorded in both V. dahliae and P. capsici in the presence of MSM volatiles. There was no germination of zoospores of P. capsici or conidia of V. dahliae on PDA plates exposed to MSM volatiles after 3 days incubation. When PDA plates with zoospores or conidia, which have been exposed to MSM volatiles, were removed and placed over sterile distilled water for 3 days, no germination of zoospores or conidia was observed. These results suggest that mustard seed meal volatiles are inhibitory to P. capsici and V. dahliae, and application methods should aim at maximizing the activity of volatiles.