Influence of water potential on growth and cultural characteristics of Phytophthora cinnamomi

Abstract

The mycelium of Phytophthora cinnamomi grew along glass fibres in both sterile and nonsterile soil. Addition of glucose and yeast extract to soil significantly increased the longitudinal growth of mycelium. With water potential more negative than — 2080 kPa in the sterile soil and — 1050 kPa in the non-sterile soil there was a significant reduction in growth rate, and complete growth inhibition was recorded at approximately — 4000 kPa in both sterile and non-sterile soil. Hyphal lysis was common in all non-sterile soil treatments, this being attributed to the presence of other soil microorganisms. Sporangia were formed only in the non-sterile water controls. It is suggested that sporangia are important as inoculum in conditions of high water potential, whilst mycelial inocula are important when there are low water potentials in situations of high exogenous nutrients such as in the rhizosphere.