The resistance of Pinus radiata to infection by Macrophoma pinea

Abstract

The resistance of wounds made on Pinus radiata to infection by Macrophoma pinea was examined experimentally in the greenhouse and field. A study was made of the anatomy of the epidermal tissues of the leader and stem, of injuries of different ages, and of the recovery stages after inoculation.

There were many structural similarities between bark and wound periderm. Both provided mechanical barriers to infection by M. pinea. Wound periderm began to form 3-9 days after injury, and the mechanical barriers appeared after about 18 days. Wounds became resistant to infection after about 3-9 days, which suggests that this resistance was associated with biochemical changes in the uninjured cells lining the wound rather than with the appearance of the mechanical barrier.

Superficial injuries occluded rapidly. Wounds on fast-growing trees, however, healed slowly when the cambium was injured; the rapid growth of the xylem continually lifted the callus that was formed over the injury, providing new entry points for M. pinea. This may explain the greater incidence of malformations on very productive sites.