Dieback tolerance in eucalypt species in relation to fertilisation and soil populations of Phytophthora cinnamomi.  G.C. Marks, F.Y. Kassaby and P.C. Fagg.  December 1972.  22 pp. (unpubl.)

SUMMARY

The dieback tolerance of 16 fertilised (NPK) and unfertilised eucalypt and two conifer species was tested in the coastal forests of east Gippsland on sites rated as “high”, “moderate” and “low” hazard on the basis of previous dieback in the forest, internal drainage in the soil, and infection by P. cinnamomi. Measurements were made of the Population Density Index (PDI) of P. cinnamomi, soil moisture, and soil temperature. Supporting greenhouse and laboratory experiments are also reported.

The high-hazard site showed the most uniform infection and the greatest PDI, while the low-hazard site the least uniformity in infection pattern.

During the first year’s growth, five eucalypts of the sub-generic group Renantherae showed considerable sensitivity to dieback, and the intensity of the disease and the number of deaths was directly proportional to the hazard rating of the sites. The eleven species of Macrantherae tested were very tolerant to dieback.

The disease was aggravated in this first year by temporary water logging during a seven-day period, but this did not cause dieback. The disease first appeared in the plots when soil temperatures rose above 15°C. Greenhouse tests showed that P. cinnamomi is most virulent at 22°C, and visible injury becomes evident between 15° and 18°C.

Fertilisers produced striking growth responses during the first year in all eucalypts on the low-hazard site, and there were only minor differences between the two sub-generic groups. Similar responses were seen only in the Macrantherae on the moderate and high-hazard sites. On these, growth of the surviving Renantherae was uneven, and fertilisers greatly increased their sensitivity to dieback. The response to fertilisation in both sub-genera was directly proportional to the disease hazard of the site and the intensity of infection by P. cinnamomi. The differences, in the response to fertilisation, between the Macrantherae and their Renantherae was directly proportional to the intensity and distribution of P. cinnamomi in the soils.

The initial dieback tolerance of the two conifers, Pinus radiata and P. elliotti, was similar to the most tolerant of the eucalypts.

Also published:

Marks, G.C., Kassaby, F.Y. and Fagg, P.C. (1973)  Dieback tolerance in eucalypt species in relation to fertilisation and soil populations of Phytophthora cinnamomi.  Aust. J. Bot. 21 (1): 53-65.