Does red coloration in tropical young leaves limit damage by a fungal pathogen?
Many tree species in the humid tropics flush their canopy in brightly colored young red leaves. Many hypotheses presented to explain the adaptive significance of this phenomenon including protection against photoinhibition, screening against ultra violet radiation, and defense against herbivores. In the tropics, attack by pathogenic fungi is a potentially important source of mortality during the vulnerable period of leaf expansion. Previous work suggested that the anthocyanin pigments responsible for the red coloration may play a role in protecting young leaves against leaf-attacking fungal pathogens, but little follow up work has been conducted to support this hypothesis.
In the summer of 2014 we inoculated 60 young leaves of 5 different tree species from Parque Nacional San Lorenzo in the Republic of Panama with the generalist fungal pathogen Calonectria sp. We assessed the relationship between pathogen damage and anthocyanin content in young leaves.
Our results showed a significant negative relationship between pathogen damage and anthocyanin content in young leaves, and significant variation in pathogen damage among tree species. Our work supports the hypothesis that anthocyanin pigments play an antifungal role for developing young leaves and provides a more complete understanding for the adaptive role of red coloration in tropical forests.