Development of Phytophthora cinnamomi infection in roots of Eucalyptus spp. growing in a soil that suppresses phytophthora root disease.  G. C. Marks and I. W. Smith.  June 1983.  11 pp. (unpubl.)

SUMMARY

When Eucalyptus sieberi L. A. S. Johnson (silvertop) was grown in either a steamed or unsteamed krasnozem that suppressed Phytophthora cinnamomi Rands root rot and repotted when either six or twelve weeks old in a larger container of inoculated sandy loam, seedling survival was significantly greater in the unsteamed treatments. By varying the treatments in the inner core soil and outer inoculum jacket, substituting a biologically inert coarse sand in place of the krasnozem in the core, and using eucalypt species of varying disease tolerance, while maintaining strict hygiene conditions throughout these experiments, it was possible to either demonstrate or deduce that:

1. the seedlings were killed when infection spread into the major roots, root collar and lower stem;
2. the microflora in the unsteamed krasnozem appeared to slow down the decay process within the root, possibly at the time the fungus was attempting to establish itself within the root;
3. the phenotypic resistance of a seedling to root disease depended, inter alia, on its genetic resistance and on the microflora in the surrounding soil; and
4. once the fungus was established in the suberised tissues, the microflora in the external environment had no influence on further movement of the fungus within the root.

Also published:

Marks, G.C. and Smith, I.W. (1983) Development of Phytophthora cinnamomi infection in roots of Eucalyptus spp. growing in a soil that suppresses phytophthora root disease.  Aust. J. Bot. 31: 239-45.