DISTRIBUTION OF MATING TYPES AND THE NATURE OF SURVIVAL OF PYTHIUM-SPLENDENS IN SOIL

Among 124 isolates of Pythium splendens obtained from field soils, 91 were ( + ) and 33 were ( - ) mating type. About 94% of these isolates existed in soil as spherical propagules with diameters ranging from 10 to 44 mum. P. splendens produced only sporangia with diameters ranging from 10 to 39 mum on agar media and in infected seeds buried in naturally-infested soil, indicating that the survival structures observed were sporangia. None of the isolates tested originated from oospores and oospores were not found in seeds concomitantly colonized by both mating types of P. splendens in naturally-infested soil. Under natural conditions in the field, 1 g dry soil contained 24-477 sporangia.