Histopathological analysis of the Rubus idaeus - Aculeastrum americanum interaction and climate change impacts on late leaf rust monocyclic components and primary metabolism of raspberry plants

• Ano de defesa: 2025
• Autor(a) principal: Barbosa, Lucas Henrique Santos
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Pucciniastrum americanum; Thekopsora americana; Abiotic stress; Estresse abiótico; Framboesa; Interação planta-patógeno; Plant-pathogen interaction; Raspberry
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/11/11144/tde-08082025-154857/

Raspberry late leaf rust, caused by Aculeastrum americanum (Farl.) M. Scholler & U. Braun has been reported in several countries. All aerial parts of the plant can be infected, with the primary symptoms of this disease being powdery yellow spots. Lesions reduce leaf gas exchange and lead to early defoliation. Moreover, infected fruits become unmarketable, resulting in severe yield losses. Despite the growing threat of this rust, the histopathology of A. americanum on raspberry remains poorly understood, particularly on Rubus idaeus L., one of the widely cultivated and economically important raspberry species. These knowledge gaps are even more critical in the context of climate change, as drought reduces host resistance and allows the emergence of pathogens that benefit from changes in plant physiology under water stress. However, for pathogens that penetrate only via the stomata, like A. americanum, stomatal closure due to water stress can prevent infection. Increased temperature poses a significant threat, including increasing pathogen abundance, shortening incubation periods, and expanding the geographic ranges of many pathogens. Thus, the present study aimed: (1) address a critical knowledge gap regarding the histopathological features of the Rubus idaeus - Aculeastrum americanum interaction; (2) evaluate the monocyclic components of late leaf rust and the primary metabolism responses of raspberry plants under water deficit conditions following pathogen infection; and (3) investigate the impact of high temperature on the monocyclic components of late leaf rust and the structural and primary metabolism responses of raspberry plants. This study elucidates the infection, colonization, and reproduction processes of A. americanum on raspberry leaves. Additionally, it provides new insights into chloroplast-pathogen interactions and, for the first time, demonstrates the formation of more than one haustorium within a single host cell by a rust. The study also showed that the occurrence of water deficit after the onset of infection by the pathogen leads to a reduction in disease severity, since the plant\'s photosynthetic activity is impaired. This results in lower production of photoassimilates, limiting the supply of nutrients to the pathogen and, consequently, its colonization capacity. Additionally, the increase in air temperature reduces the infection efficiency of A. americanum due to stomatal closure, with the disease damage being more pronounced at 25 °C than at 30 °C.