P-657 - Infection of the clonal Japanese knotweed plant Fallopia japonica by Lasiodiplodia sp. and its mode of spread

Theoretical studies suggest that pathogens spread more easily through ramets in clonal plants due to their morphological and physiological characteristics. However, empirical studies on infection patterns are limited. In this study, we examined the likelihood of seed transmission and infection spread through ramets using Japanese knotweed, a clonal plant designated one of the world's worst invasive alien species by the International Union for Conservation of Nature (IUCN) in 2000, and Lasiodiplodia sp., a fungus that causes spot symptoms but never produces pseudothecia or spors outside of the plant. Germination experiments using seeds from infected ramets produced healthy individuals from both surface-sterilized and unsterilized seeds. This suggests that fungal transmission via the endosperm or embryo inside the seed coat is rare. Additionally, small brown spots were observed in all young ramets derived from the aboveground stems of infected ramets. Furthermore, fungi belonging to the genus Lasiodiplodia were isolated from the internal tissues of the aboveground stems near the base of infected ramets. Based on these findings, while seed transmission cannot be completely ruled out, the primary infection pattern in Japanese knotweed is considered to be fungal hyphae spreading through aboveground stems or rhizomes.