Abstract:
The increasing threats from pests and diseases demand that the South African
forest industry explores options to deploy alternative pine species in plantation development.
This is especially true for species, such as Pinus patula Schiede and Deppe ex
Schltdl. and Cham., which are highly susceptible to the pitch canker fungus Fusarium
circinatum. Losses due to F. circinatum have been confined mostly to nurseries and at field
establishment resulting in a significant cost to the industry. Although, the fungus has not as
yet resulted in stem and branch infections on established P. patula in South Africa, it has
caused pitch canker on other, more susceptible species such as P. radiata D. Don., and
P. greggii Engelm. ex Parl. As alternatives to P. patula, on the warmer and cooler sites in
South Africa, families of P. elliottii Engelm var. elliottii, P. tecunumanii (Schw.) Eguiluz
and Perry, P. maximinoi H. E. Moore and P. pseudostrobus Lindl. were screened for
tolerance to infection by F. circinatum in greenhouse studies. Seedlings were wounded and
inoculated with spores of F. circinatum. Lesion development following inoculation was
used to differentiate the levels of tolerance between families. The results showed that
P. maximinoi, P. pseudostrobus, and the low elevation variety of P. tecunumanii are highly
tolerant to infection with very little family variation. The narrow sense heritability estimates
for these species were less than 0.06. In contrast, P. elliottii showed good tolerance
with some family variation and a heritability of 0.22, while the high elevation source of
P. tecunumanii showed a high degree of family variation and a heritability of 0.59.
These results provide the industry with valuable information on pine species tolerant to
F. circinatum that could be used as alternatives to P. patula in South Africa.
