PITCH CANKER DISEASE IN CALIFORNIA - PATHOGENICITY, DISTRIBUTION, AND CANKER DEVELOPMENT ON MONTEREY PINE (PINUS-RADIATA)

Pitch canker disease, caused by Fusarium subglutinans, has become prevalent on Monterey pine (Pinus radiata) in several central and southern coastal counties of California. Although Monterey pine is the most frequently infected host, the pathogen has also been recovered from bishop (P. muricata), Aleppo (P. halepensis), and Canary Island (P. canariensis) pine. All 167 isolates of F. subglutinans recovered from diseased tissue, insects, and air samples in California were virulent on Monterey pine in greenhouse pathogenicity tests, and 63 pine isolates of F. subglutinans from Florida, North Carolina, and Texas were also virulent on Monterey pine. All isolates of F. subglutinans from plant hosts other than pine, as well as pine and nonpine isolates of F. proliferatum and F. moniliforme, were avirulent or weakly virulent on Monterey pine and considered nonpathogenic. Airborne inoculum of F. subglutinans was detected throughout the year in Santa Cruz Country in an area with a high incidence of pitch canker disease but was not detected in an area where the disease was absent. F. subglutinans was also recovered from numerous insect species in this area, many of which are capable of feeding on Monterey pine and causing wounds. Inoculation data in this study provide considerable justification for assigning strains of F. subglutinans pathogenic to pines to a specific forma specialis. We therefore propose that the pitch canker pathogen be designed F. subglutinans f. sp. pini. Isolations and field inoculations indicated that different aged branch tissue, cones, and boles were susceptible infection courts throughout the year. Extensive resin-soaked cankers developed from branch and bole inoculations in less than 2 yr. The significant differences in canker development observed among field-inoculated Monterey pine trees may reflect genetic variation in susceptibility to pitch canker disease within the population of planted Monterey pines in California.