The effect of moisture stress in Eucalyptus sieberi on Phytophthora cinnamomi lesion development.  I. W. Smith and G. C. Marks.  October 1985.  9 pp. (unpubl.)

SUMMARY

Moisture-stressed and unstressed twelve-month-old seedlings of Eucalyptus sieberi L.A.S. Johnson (silvertop), grown in a controlled environment, were wound-inoculated with and without mycelium of Phytophthora cinnamomi Rands (cinnamon fungus) and the extent of lesion development measured.

In addition, five-year-old saplings of E. sieberi, some released and others unreleased from the competitive effects of growing in a dense regenerating stand, were also inoculated with P. cinnamomi and subsequent lesion development measured.

The degree of stress was determined using leaf water potential measurements.

Stem lesions developed only on seedlings inoculated with P. cinnamomi. The length and area of lesions were significantly greater on seedlings and saplings that were not subject to moisture stress. Leaf water potentials of excised leaves of stressed seedlings and unthinned saplings were significantly lower for pre-dawn measurements than those from the unstressed and thinned treatments. Midday water potentials were significantly lower for stressed seedlings than unstressed seedlings, but not for thinned and unthinned saplings in the field. Soil moisture potentials were significantly lower in unthinned plots.

The hypothesis that high water potentials are required for lesion development as well as initial infection has important implications for disease control. In forest areas with high potential disease risk, the benefits of forest practises such as thinning and selective logging need to be weighed against the possible increase in disease activity due to greater water availability.

Also published:

Smith, I.W. and Marks, G.C. (1986)  Effect of moisture stress in Eucalyptus sieberi on growth of lesions caused by Phytophthora cinnamomi.  Aust. For. Res. 16 (3): 273-279.