Suppression of Fungal Pathogen Phytophthora capsici by Mycophagous Soil Fauna.

Predation of fungal pathogens by mycophagous soil fauna is believed to play an important role in the suppression of plant diseases. However, there is a limited amount of direct evidence demonstrating faunal controls over soilborne pathogens. We evaluated the roles of collembola and nematodes in regulating the population dynamics and pathogenic activity of Phytophthora capsici in three different soils, using pepper-P. capsici as a model pathosystem. Soils were defaunated, and then inoculated with P. capsici, collembola (Hypogastrura perplexa or Sinella curviesta), and nematodes (Aphelenchus avenae) in various combinations. Pepper seeds were planted one week after pathogen inoculation, and the seedling mortality was then examined weekly. Pathogen density and faunal populations were assessed 21 days after seeding. The number of H. perplexa significantly increased by up to 41-fold, but the magnitude of the increase was found to be lower in the clay soil than in the sandy and loamy ones. The population of A. avenae significantly increased in both the clay soil and the sandy loam, but not in the loamy soil. Compared to the non-faunal control, introducing soil animals reduced the population of P. capsici by between 50 to 85%. Soil fauna significantly reduced disease incidence on pepper and soil type significantly affected the efficiency of faunal suppression. Compared to their corresponding controls, disease incidence in the faunal treatments was reduced by 8.9-27% in the clay soil, 71-96% in the loamy soil, and 84-99% in the sandy loam, respectively. These results suggest that soil mesofauna might be managed for suppression of seedling diseases caused by soilborne pathogens.