Ontogeny of Phyllosticta ampelicida mummies from autumn to spring

Abstract: In order to enhance our comprehension of black rot epidemics in grapevines, we
conducted three-year experiments to study the ontogeny of conceptacles into berries which were mummified by Phyllosticta ampelicida. In the first experiment, (November 2022 to May 2023), berries were of Ugni blanc grape variety, whereas in the second experiment, (December 2023 to June 2024), they were of Floreal grape variety. For the last experiment, berries were of Artaban and Prior grape varieties (July 2024 to May 2025). Mummified berries were sampled regularly after rain and frozen at -20 °C before being cut with a freezing microtome. Sections of conceptacles taken from mummies were examined under a microscope in order tocharacterize the different conceptacles observed. They were classified into six morphological types: empty; pycnidia; spermogonia; undifferentiated; beginning of structuration; and perithecia. Combining the information from all these studies enabled to study the ontogenesis of perithecia and pycnidia inside the mummies and showing similarities to what had been achieved in vitro. By describing the time-course curve of the different categories during a season, hypotheses were built for the possible transitions from one type to another. We observed a decrease in undifferentiated conceptacles over the course of the season, alongside a gradual increase in perithecia from January until a peak in March/April. It seems that pycnidia are produced quickly after mummification, but the phenomenon is not long lasting.