Abstract:
Fusarium circinatum is an important fungal pathogen of Pinus species. In South Africa, it is the most significant
pathogen of Pinus patula seedlings in forestry nurseries where it presents a substantial constraint to productivity
and can continue to cause mortality in-field for up to two years after establishment. This study describes
the results from two trials where P. patula seedlings were inoculated with F. circinatum to determine the impact
of the pathogen on nursery and field performance. Seedlings were also subjected to water stress treatments to
ascertain whether this would trigger the onset of disease symptoms. Inoculum load and timing of inoculation
had significant effects on seedling survival in both the nursery and field. High inoculum concentrations caused
greater levels of mortality and, where seedlings were inoculated at a young age, they showed higher levels of
susceptibility to F. circinatum. Temporary water-stress in the nursery produced smaller plants and improved
in-field survival, but this treatment did not trigger higher mortality in inoculated treatments. On the other hand,
transplant stress was a major contributor to the higher levels of mortality observed in inoculated treatments.
Overall, these studies confirmed that infection in the nursery leads to the disease problems observed during early
plant establishment in the field.
