Pitch Canker in California Mediterranean Conifer Systems

Abstract

Fusarium circinatum, the cause of pitch canker in pines, is a recent introduction to California, most likely on seeds from the southeastern United States. The most common symptom of pitch canker is branch dieback that results from a lesion, usually within one or two whorls of a branch tip, that girdles and kills the affected branch distal to the point of infection. The success of F. circinatum as a pathogen of pines in coastal California can be attributed to: (1) an abundance of highly susceptible host trees, (2) a climate that provides conditions suitable for infection throughout much of the year, and (3) a relationship between the pathogen and native insects that can transport the fungus and create infection courts. Systemic induced resistance (SIR) to pitch canker has been documented in P. radiata. Trees in areas where pitch canker was well established were significantly less susceptible to the disease than trees in areas where pitch canker was a more recent occurrence. SIR may be an important part of the explanation for stabilization of pitch canker in Monterey pine forests and can help to explain, how long-lived perennials have survived infection by parasitic microbes that have generation times orders of magnitude shorter than their host plant.