Structural and physiological implications of witches' broom infection in Xylopia aromatica (Annonaceae) trees

Abstract

Witches' brooms are abnormal branches that can affect various tree species in the Brazilian savanna, such as Xylopia aromatica. This disease leads to biomass loss and alters growth patterns. This study investigated the anatomical and physiological impacts of witches' broom on X. aromatica, hypothesizing that the disease induces changes in both infected and noninfected branches of the same tree. Measurements included leaf area, chlorophyll content and photosystem II (PSII) functionality in control and infected plants, as well as branch types (control, uninfected and infected branches for infected plants). Water potential was assessed at predawn and midday, and stem samples were analysed for anatomical and vessel element analysis. Witches' broom disease manifests as short brown stems and small yellowish‐green leaves. While infected and uninfected plants showed no significant differences in leaf area and leaf dry biomass, infected branches had reduced leaf number, area and weight. Chlorophyll content and PSII efficiency were significantly reduced in infected branches, indicating photosynthetic disruption. Water potential was lower at predawn in infected plants but normalized by midday, suggesting an adaptive response. Anatomical changes in infected branches included alterations in vessel elements and parenchymatic rays. Overall, X. aromatica displays localized changes due to witches' broom, which aids in water stress adaptation. Despite these findings, long‐term studies are needed to evaluate the impacts on biomass reduction and reproductive investment in Brazilian savanna areas, crucial for understanding the ecological impact and developing survival strategies for affected plants.