Pathogenicity of Phythium spp. and Phytophthora drechsleri to Eucalyptus spp.  G.C. Marks and F.Y. Kassaby.  April 1974.  9 pp. (unpubl.)

SUMMARY

A number of Pythium spp. and Phytophthora drechsleri have been associated with Phytophthora cinnamomi in the die-back diseases of eucalypts, in forests of southern and eastern Australia. Although Phytophthora cinnamomi is generally considered to be the most important pathogen causing root rot and die-back, there is some uncertainty whether it is the only pathogen.

The pathogenicity of Pythium ultimum, P. debaryanum, P. vexens, P. mammalatum, three unidentified Pythium species from eucalypt forest soil and Phytophthora drechsleri, was compared with that of Phytophthora cinnamomi using juvenile and intermediate aged seedlings of Eucalyptus sieberi and juvenile seedlings of other eucalyptus spp. Of the Pythiums, only P. ultimum, P. irregulare and P. debaryanum could kill small juvenile seedlings in the two-leaf stage of development. Neither any of the Pythiums nor Phytophthora drechsleri could kill E. sieberi in the intermediate growth stage. In marked contrast, Phytophthora cinnamomi showed considerable pathogenicity killing seedlings and saplings with rapidity. The unidentified Pythium spp. from native forest were completely innocuous.

Also published:

Marks, G.C. and Kassaby, F.Y. (1974)  Pathogenicity of Phythium spp. and Phytophthora drechsleri to Eucalyptus spp.  Aust. J. Bot. 22 (4): 661-8.