Poinsettia cuttings increase resistance to Botrytis cinerea infection over time in propagation

Commercial poinsettia production in the United States (US) begins with the propagation of unrooted cuttings that are harvested from stock plants. Unrooted cuttings are produced in Mexico and Central America and shipped to the US via airfreight. During propagation, Botrytis blight caused by Botrytis cinerea can reduce the quality and viability of poinsettia cuttings, leading to leaf loss and tissue collapse. Cuttings appear to be more prone to the development of Botrytis blight during the initial days in propagation; however, there are no data to support this observation. The objective of this project was to evaluate if the susceptibility of poinsettia cuttings to Botrytis blight changes during propagation. Two experiments were conducted with three repetitions over time for each. During the first experiment, poinsettia cuttings were inoculated with a spore suspension of Botrytis cinerea (1×10⁴ spores mL^‑1) after 0, 2, and 4 d in propagation. For the second experiment, cuttings were inoculated after 0, 3, 6, and 9 d in propagation. For both experiments, the cuttings were placed in humid chambers following inoculation, and Botrytis blight development was assessed over a period of 15 d. Additionally, non-inoculated cuttings of each treatment were placed in the humid chambers simultaneously with the inoculated cuttings to evaluate ambient disease pressure. For both inoculated and non-inoculated cuttings, Botrytis blight severity decreased linearly as cutting time in propagation increased. Overall, 9-day-old cuttings showed 54% of reduction in Botrytis blight severity in comparison to 0-day-old cuttings. These results indicate that the age of poinsettia cuttings is linked to the susceptibility to Botrytis blight severity, and cuttings are most susceptible to Botrytis infection immediately following harvest. Further investigations are required to elucidate the physiological, biochemical, and molecular mechanisms behind this response, which may reveal alternative approaches for disease management.