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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.

In response to theFusarium circinatum pine pathogen threat in Southern Africa, research has been conducted on the development of F. circinatumtolerant P. patula and P. patula hybrids. The objective of this study was to investigate the propagation potential of these taxa in two vegetative propagation systems, hydroponic sand beds and polythene bags with composted pine bark growing media. Significant differences (p < 0.001) in mortality associated with F. circinatum were observed between the P. patula x P. tecunumanii (LE) hybrid (6%) and P. patula (19-23%). No significant differences in mortality associated with F. circinatum were observed within P. patula x P. tecunumanii (LE) families which ranged from zero to 15 percent. Significant mortality differences (p < 0.001) were observed between P. patula families which ranged from eight to 44 percent. The number of rooted cuttings produced, per hedge established, over the four year period was significantly better (p < 0.001) in the P. patula x P. tecunumanii (LE) hybrid (52) than in P. patula (29-33). Significant differences (p < 0.001) were also observed in the number of rooted cuttings produced per family, with P. patula x P. tecunumanii (LE) families ranging from 35 to 70 cuttings per hedge plant established and P. patula families between 20 and 42 cuttings. Over the four year duration of the trial all taxa showed increased productivity in hedges grown in a hydroponic sand bed system, which received more consistent fertilisation and yielded an average of 55 rooted cuttings per hedge, over those grown in polythene bags with composted pine bark medium which yielded 41 cuttings on average. This study demonstrated that the P. patula x P. tecunumanii (LE) hybrid is a feasible substitute for P. patula in both vegetative propagation systems, as it not only shows improved survival, through increased F. circinatum tolerance, but also improved productivity.

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