Prolonged periods of flooding increase susceptibility of <i>Gordonia lasianthus</i> to <i>Phytophthora cinnamomi</i>

Phytophthora cinnamomi is a globally important soilborne Oomycete plant pathogen with an extensive and diverse host range, including numerous tree species and woody ornamental plants, and has disrupted forest ecosystems on multiple continents. Members of the Gordonieae tribe, in the family Theaceae, exhibit varying degrees of susceptibility to P. cinnamomi, with Franklinia alatamaha likely being extinct in nature because it is very susceptible to this pathogen. In contrast, Gordonia lasianthus, or loblolly bay, was previously considered resistant when compared to other Gordonieae species. However, in 2019, bleeding cankers were observed on the lower trunk of mature G. lasianthus trees in a coastal forest in South Carolina, in an area that experienced extensive flooding likely due to a recent hurricane and anthropogenic development. This study demonstrates how prolonged exposure to flooded soil conditions significantly increased susceptibility of G. lasianthus to P. cinnamomi and led to severe symptoms of wilting, defoliation, and mortality. It also suggests how host-pathogen interactions involving species of Phytophthora may shift in the future because of climate change and increased frequency of extreme weather events.