USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

1731 Research Park Dr.
Davis, CA 95618
(530) 759-1700
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Slow-rusting Resistance (SRR)

Low Infection Frequency
Individual trees vary greatly in frequency of infection from equivalent amounts of inoculum: tree at left has many infections, compared with tree at right.
Bark Reaction (BR)
Infection grows normally and symetrically into bark tissues from the primary infection court in a needle (arrow). The sudden collapse of the infected tissues is a 'bark reaction'. Necrotic tissue is surrounded by healthy wound periderm (right), which will eventually heal the lesion.
Variation in size of bark reactions.
The rate (and therefore size) of BRs vary greatly. Note continued fungal activity on the large BR on left (arrow). Note needle trace at center of small BR at right
Bark reaction on a branch of sugar pine. Note healthy tissue on either side.
Blight Reaction
Another kind of reaction that resists spread of fungus into the bole is a rapid blighting of the entire shoot distal to the infection site. Bark reaction , in contrast, are local lesions with green tissue both distal and proximal to the infection site.