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Model Simulations of Infection of Douglas-Fir Seedlings by Fusarium oxysporum. W. J. Bloomberg, Forest pathologist, Environment Canada, Canadian Forestry Service, Pacific Forest Research Centre, Victoria, B.C. V8Z 1M5; Phytopathology 69:1072-1077. Accepted for publication 5 April 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-1072.

A simulation model of Fusarium root rot of Douglas-fir seedlings was used to predict seedling infection, mortality, root growth in various temperature regimes, root growth rates and sizes, and concentrations of inoculum. The most important factors in simulated root infection were those affecting size and number of infection sites (root tips), size and concentration of inoculum particles, and rate of lesion elongation. More and longer root tips per seedling, more infections, more rapid spread of lesions in roots, and more seedling mortality were predicted by simulations with warm regimes than by those with moderate or cool regimes. Simulations with fast root growth rates also predicted more and longer root tips and infections than did those with slow or moderate root growth rate but no increase in rate of lesion spread or seedling mortality. Simulations with relatively long or thick inoculum particles or relatively dense inoculum concentrations predicted more root infection and seedling mortality than did those with small particles or sparse concentrations. According to model predictions, density of inoculum in the upper 10 cm of soil had a greater effect on infection and seedling mortality than density in the lower 10 cm. The rapidity with which the taproot became infected and the proximity of infections to the upper part of the taproot were the most important factors in seedling mortality. Predicted root length was affected most by rate of root elongation, number of infections and rate of lesion elongation.

Additional keywords: Computer, late damping-off, nursery disease.