Association of the pitch canker fungus, Fusarium subglutinans f.sp. pini, with Monterey pine seeds and seedlings in California

The causal agent of pitch canker disease of pines, Fusarium subglutinans f.sp. pini, is a recent introduction to California. The work presented here demonstrates that this pathogen is seed‐borne in Monterey pine (Pinus radiata). The pathogen was isolated from up to 83% of seeds collected from cones on recently infected branches. Seedling emergence from infested Monterey pine seeds was 9%, compared with 67% for uninfested seeds. The fungus was isolated more frequently from seedlings originating from diseased branches than from symptomless branches. However, more than 50% of seeds from symptomless Monterey pine branches produced symptomless seedlings from which the pathogen was isolated. It is hypothesized that F. s. pini is carried within the seeds, where it may remain dormant until germination. The implications of these findings for the regeneration of native and landscape‐planted Monterey pines, and for the transport of this non‐native pathogen in pine seeds and seedlings to previously uninfested areas, are discussed.