Comparison of the mycoparasites Pythium periplocum, P. acanthicum and P. oligandrum

Abstract

Mycoparasitism by Pythium periplocum, a species with spiny oogonia, was evaluated and compared on several host fungi with parasitism by P. oligandrum and P. acanthicum on the same fungi. These species were found to be aggressive mycoparasites with a wide host range. Differential reaction among some of the hosts tested were found in relation to each mycoparasitic species. Thirty isolates of each of these species, obtained from diverse agricultural soils in California were further studied. Pythium ultimum, one of the most susceptible hosts for the three species, in an in vitro test of mycoparasite virulence, was slightly susceptible, moderately susceptible, and highly susceptible to most of the isolates of P. acanthicum, P. oligandrum and P. periplocum tested, respectively. In one test, sugar beet seedlings were protected from damping-off due to P. ultimum by co-inoculation of seedlings with P. periplocum or P. oligandrum. In the same in vitro test P. acanthicum gave no protection against P. ultimum. The degree of disease protection varied among isolates within each mycoparasitic species studied. As part of the study each mycoparasitic isolate was critically characterized by the morphology of oogonia, oospores, oogonial spines, sporangia and the rate of daily growth of mycelium at 25 °C. Pythium periplocum was readily separated from the other two species by its lobate sporangia and size of the oospore. Pythium oligandrum could be separated from P. acanthium by its acutate oogonial spine apex, longer spine and faster growth rate.