How container media and matric potential affect the production of sporangia, oospores and chlamydospores by three phytophthora species

Abstract

Miracloth discs containing Phytophthora cinnamomi, Phytophthora cilricola and Phytophthura drechsleri were exposed to matrie potentials ( ψ m) between 0 and 10 kPa. in a composted Eucalyptus-bark mix (CEB) which was apparently suppressive to disease and a nurseryman's mix (NM) which was apparently conducive to it. The CEB and NM stimulated P. cinnamomi and P. cirechsleri to produce sporangia. The CEB suppressed indirect germination of both species. P. cilricola required an exposure period of 10 days before sporangia formed, which were produced in significantly higher amounts at −5 and −7.5kPa in the NM. P. cinnamomi and P. drechsleri produced more sporangia as ψ m decreased. Chlatnydosporcs produced by P. cinnamomi were lysed in both media at 0 and −1.0 kPa, but at matric potentials below −2.5 kPa they were lysed only in the CEB. Oospores of P. citricola were produced only up to 7 days in both media at ψ m below −2.5 kPa. Bacteria and actinomycetc filaments were closely associated with all propagules of the three Phytophthora spp in the CEB. They were most evident at matric potentials < −2.5 kPa.