Abstract:
The leaf and shoot blight disease known locally as Daño Foliar del Pino (DFP) is the
most important problem affecting Chilean Pinus radiata plantations. The disease is
typified by needle infections, exudation of resin at the bases of needle brachyblasts and
necrotic lesions in the cambium of younger trees, which eventually girdle branches. The
disease causes death of seedlings young trees and mature trees can also succumb after a
few years of successive infection. DFP emerged very recently and its cause was
unknown. Studies that make up this thesis led to the identification of the causal agent of
DFP, which was described as the new species Phytophthora pinifolia A. Durán,
Gryzenh. & M.J. Wingf. This is the first discovery of a Phytophthora sp. infecting
needles and shoots of a Pinus sp. anywhere in the world. Two diagnostic procedures
were developed to screen large numbers of samples rapidly and cost effectively for the
pathogen. Population genetic studies showed that the P. pinifolia population in Chile is
a single clonal lineage that exists in the absence of sexual recombination. This suggests
strongly that P. pinifolia is an introduced pathogen in Chile although its origin and
natural host-range is uknown. In order to promote effective management of P. pinifolia,
three fungicides were screened in vitro and in planta. Mefenoxam was shown to be the
most effective compound, also providing the most consistent results. DFP is recognized
as one of the most important disease problems to strike non-native pine plantation
forestry in recent times. Studies in this thesis represent the first ever on the disease and
its causal agent and they provide a foundation for the many studies that must follow to
ensure that P. pinifolia does not lead to disease disasters elsewhere in the world.
