Abstract:
In recent years, Pinus plantation forestry has been significantly hampered by outbreaks of
pitch canker caused by the fungus Fusarium circinatum. In this study we investigated the role
of Pinus host, geographic origin and reproductive mode in structuring the F. circinatum
populations in plantations. For this purpose, 159 isolates originating from diseased plantation
trees in the Western and Eastern Cape Provinces of South Africa, were genotyped using 10
microsatellite markers. Analyses of these data revealed 30 multilocus haplotypes and that the
populations were distinct based on geographic origin as well as host. However, shared
haplotypes were observed between populations, showing that these populations are connected
possibly through the movement of haplotypes. A second aim was to determine whether the
genetic variation found in these populations of the fungus could be attributed to outbreaks of the seedling disease caused by this pathogen in Pinus nurseries. To achieve this goal, an
additional set of 43 isolates originating from pine seedling nurseries were genotyped and
analysed. The results showed that the populations of F. circinatum in plantations most likely
originated from the nursery outbreaks that occurred prior to the plantation outbreak.
Inferences regarding reproductive mode further showed that sexual reproduction has little
impact on the genetic makeup of the F. circinatum populations and that they primarily
reproduce asexually. Overall the results of this study showed that the F. circinatum diversity
in South Africa has arisen due to multiple introductions of the pathogen and is not due to
sexual reproduction.
