Survival of Phytophthora cinnamomi in Buried Eucalyptus Roots

Abstract

AbstractColonization and survival of Phytophthora cinnamomi in roots was tested in 3 months old, axenically grown seedlings of Eucalyptus maculata (field resistant) and E. sieberi (susceptible). The roots were inoculated, then one week later were excised and buried in three non‐sterile, conducive soils; a lateritic gravel, an infertile duplex soil, a loamy sand as well as in a fertile, suppressive krasnozem. Pathogen viability, percentage root colonization and chlamydospore numbers were examined at matric potentials of −1/3, −5 and −10 bar after periods of 10, 100 and 200 days at 21°C.At 10 days, survival was 100% in the form of mycelium and the only significant difference was between the two Eucalyptus species. At 100 days survival was solely due to chlamydospores, but the pathogen was viable in all inoculated roots and at each matric potential. At 200 days soils had dried to less than −10 bars and the pathogen failed to survive. No significant differences were found between the two pathogen isolates but significant differences were obtained between the susceptible and field resistant Eucalyptus species.Pathogen viability, percentage root colonization and chlamydospore number were highly correlated with soil types and matric potential. These components declined with decreasing soil matric potential. The Krasnozem was only suppressive at relatively high soil matric potentials (−1/3 bar). At lower values (−5, −10 bar) survival of the pathogen, chlamydospore numbers and percentage colonization of the roots in the Krasnozem were comparable with that of the 3 conducive soils tested.Chlamydospores were present, but in low numbers in roots buried in the suppressive soil at −1/3 bar.