Effects of Nitrogen, Phosphorus and Calcium Nutrition on Growth of Eucalypt Seedlings and on the Expression of Disease Associated With Phytophthora cinnamomi Infection

Abstract

In glasshouse trials, seedlings of Eucalyptus maculata and E. pilularis, grown in sand and supplied with independently varied levels of nitrogen, phosphorus and calcium, were inoculated with Phytophthora cinnamomi. The response of the seedlings was evaluated 9 weeks after inoculation.

Seedling growth (height, shoot and root dry weight) increased with increasing levels of nitrogen and phosphorus supplied to the plant. Increased calcium levels produced an increase in shoot weight only when phosphorus levels were high. High levels of both nitrogen and phosphorus produced a synergistic increase in growth.

Inoculation with P. cinnamomi caused a significant reduction in growth in both species of eucalypt. This reduction was maximal when there was a nutritional imbalance between nitrogen and phosphorus and minimal when nitrogen and phosphorus levels were balanced and the plants were growing vigorously. The pathogen was recovered most frequently from seedlings growing on low levels of nitrogen and phosphorus, indicating that P. cinnarnomi is less successful in infection or survives in the root for a shorter period when nutritional conditions favour vigorous growth.

The form in which nitrogen was supplied also affected seedling growth; maximum growth was obtained when the nitrate to ammonium nitrogen ratio was 7 : 3. The form of nitrogen supplied did not affect the response to inoculation with P. cinnamomi.