The principal objective of this research has been to reduce the potential impact of Fusarium
circinatum on young and mature Pinus patula trees in South Africa. The results provide new
knowledge concerning the genetic variation within P. patula, and suggest alternative species and
hybrids, with resistance to infection by the pitch-canker pathogen F. circinatum. The infection
of nursery plants is the principal cause of dying seedlings after planting and controlling the
disease in the nursery is paramount to achieving good post-planting survival of P. patula. A large
number of alternative pines, which are more tolerant to the pathogen, exist. Pinus elliottii is the
most versatile alternative due to the ready availability of seed and the fact that it can be planted
on a wide range of sites. Although the species is more tolerant than P. patula, individual families
vary in their tolerance to F. circinatum and care should be taken to eliminate the more
susceptible families. Pinus maximinoi and the low elevation (LE) source of P. tecunumanii are
highly tolerant and provide an excellent alternative to P. patula on sites free of frost. The high
elevation (HE) source of P. tecunumanii, which is more tolerant of cold than the low elevation
source, is significantly more tolerant to F. circinatum than P. patula. However, large variation in
the tolerance of individual P. tecunumanii (HE) families to F. circinatum exists and tolerant
families of this source need to be identified before commercial deployment. Although P.
maximinoi and P. tecunumanii are sub-tropical pines and sensitive to frost, meaningful variation
in the tolerance of individual families to frost has been observed which indicates that these
species can be bred for improved frost tolerance. On the colder sites, P. pseudostrobus may
become an important alternative to P. patula due to its excellent tolerance to F. circinatum. In all
cases hybrids between P. patula and pines more tolerant to F. circinatum, are significantly more
tolerant than P. patula. Of these the P. patula x P. tecunumanii hybrid is the most promising.
Due to the excellent tolerance of P. tecunumanii (LE) all families of the P. patula x P.
tecunumanii (LE) hybrid are tolerant of F. circinatum. On the other hand, families of the P.
patula x P. tecunumanii (HE) vary greatly in their tolerance to F. circinatum and the specific
combination of the parents appears to play an important role in determining tolerance. Although
only 5% of the current P. patula growing stock is of similar tolerance to F. circinatum as P.
elliottii heritability for tolerance to F. circinatum is high in P. patula indicating that improvements can be achieved through breeding. Good control can also be achieved by
identifying specific full-sib P. patula families that are tolerant to F. circinatum, rather than the
use of open pollinated seed. It is anticipated that large areas, currently well suited to P. patula,
will in the future be replanted with pine hybrids and species more tolerant of F. circinatum.
Pinus patula, which has been bred for improved tolerance to F. circinatum, will be limited to the
most temperate regions of South Africa.