Co-Infections by and spp. on : Complex Phenotypic and Molecular Interactions.

This study investigated the complex phenotypic and genetic response of Monterey pine () seedlings to co-infections by , the causal agent of pine pitch canker disease, and the oomycetes and . Monterey pine seedlings were wound-inoculated with each single pathogen and with the combinations / and /. Initially, seedlings inoculated only with showed less severe symptoms than seedlings co-inoculated or inoculated only with or . However, 30 days post-inoculation (dpi), all inoculated seedlings, including those inoculated only with , showed severe symptoms with no significant differences among treatments. The transcriptomic profiles of three genes encoding pathogenesis-related proteins, i.e., chitinase (PR3), thaumatin-like protein (PR5), phenylalanine ammonia-lyase (PAL), and the pyruvate decarboxylase (PDC)-encoding gene were analyzed at various time intervals after inoculation. In seedlings inoculated with single pathogens, stimulated the up-regulation of all genes, while between the two oomycetes, only induced significant up-regulations. In seedlings co-inoculated with and or none of the genes showed a significant over-expression 4 dpi. In contrast, at 11 dpi, significant up-regulation was observed for PR5 in the combination / and PDC in the combination , thus suggesting a possible synergism of multiple infections in triggering this plant defense mechanism.