Abstract:
The pitch canker fungus, Fusarium circinatum, has caused large scale mortality of
young Pinus patula Schiede & Deppe ex Schltdl. & Cham. seedlings in nurseries in
South Africa since 1990. Diseased seedlings have been inadvertently carried to the
field, which in turn have died and has reduced stocking below an acceptable level. Tree
breeders have suggested that the only long-term solution to limit infection by this
pathogen is to identify and deploy tolerant P. patula families. A commonly used
technique to identify tolerant clones is to artificially inoculate open-pollinated progeny
from orchard clones with F. circinatum under greenhouse conditions. In these trials,
large variation in tolerance to the pathogen among seedlings within open-pollinated
families was observed and that this could be influenced by the pollen parent. Therefore,
identifying individual full-sib families where both parents are known, should improve the
identification of tolerant families, which can then be repeated. In this study, cuttings from
control-pollinated P. patula seedling hedges were inoculated with F. circinatum in a
greenhouse. The results showed large family variation where some of the full-sib
families were similar in tolerance to P. elliottii Engelm var. elliottii seedlings. Therefore, it
is recommended that breeders focus on identifying specific family combinations that are
more tolerant to F. circinatum.
