Investigating Biochemical and Histopathological Responses between Raspberries and .

Late leaf rust is a fungal disease in raspberries caused by (Farl.) M. Scholler U. Braun (syn. (Farl.) Aime McTaggart) leading to early defoliation and yield losses. Red raspberries ( L.) are susceptible to this pathogen, although this susceptibility varies among cultivars. In contrast, black raspberries were previously reported to be more resistant ( L.) and immune ( Thunb.) to this pathogen, raising their importance in plant breeding programs. However, what features make them respond differently to the same pathogen? In this study, we characterize for the first time the pre- and post-formed structural and biochemical defense mechanisms of cv. Autumn Bliss, and . Ultrastructural and histopathological analyses were used to uncover the interactions between these raspberries and . The ultrastructural results indicate that the pathogen germinates on both leaf surfaces but can only form appressoria on the stomata. Although the three raspberry species were infected and colonized by , a clear difference in susceptibility was observed between them. A compact mesophyll, pre- and post-formed phenolic compounds, and post-formed pectic compounds were the main plant defense mechanisms against fungal colonization. These findings provide new information about raspberries' defense mechanisms in response to and elucidate the interactions occurring in these pathosystems.