Abstract:
Approximately 50% of the area planted to softwood trees in South Africa has been
established with Pinus patula making it the most important pine species in the country.
More effort has gone into developing this species for improved growth, tree form and
wood properties than with any other species. This substantial investment has been
threatened in the last 10 years by the pitch canker fungus, Fusarium circinatum. The
fungus infects and contaminates nursery plants and, once transferred to the field,
causes severe mortality of young trees in the first year after establishment. Although
nurserymen have some control of the disease, it is recognized that the best long-term
solution to mitigate damage due to F. circinatum infection is to identify tolerant species,
clones and hybrids for deployment in plantations in the future. Research has shown that
alternatives such as P. tecunumanii, P. maximinoi and P. elliottii are suitable for warm
sites. Pine hybrids, particularly between P. patula and the high elevation sources of P.
tecunumanii, appear to be a suitable replacement on sub-temperate and temperate
sites. Although these alternative species and hybrids are more sensitive to sub-freezing
temperatures than P. patula, their planting range can be increased by including cold
tolerance as a selection criterion. Future breeding efforts will most certainly focus on
improving the tolerance of pure P. patula to F. circinatum, which can be achieved by
identifying specific family crosses and tolerant clones. The commercial deployment of
disease tolerant control-pollinated P. patula and hybrid families will most likely be established as rooted cuttings, which requires more advanced propagation technology.
In the long term, new seed orchards comprised of P. patula clones tolerant to F.
circinatum will be used to produce seed for seedling production.
