Field survey of Fusarium stem rot of lisianthus (Eustoma grandiflorum) cultivated in Okinawa, Japan

Lisianthus (Eustoma grandiflorum) has become a major flowering plant in Okinawa, the southernmost prefecture of Japan. Its cultivation area has increased steadily with each passing year for two decades. Simultaneously, many types of lisianthus diseases related to damping-off symptoms have also increased dramatically. To create a strategy for preventing the disease, disease symptoms and pathogenic organisms of primary problematic disease with seasonal variation in the emergence were investigated. The symptoms were diagnosed as Fusarium stem rot (Kukigusare-byo) and the pathogen of the disease was identified as Fusarium avenaceum based on multigene sequences analyses. Indeed, the PCR result of the isolated strain in this study was the same as that isolated from lisianthus plants with Fusarium stem rot in Hokkaido Prefecture. Furthermore, the pathogen is clustered separately from the other F. avenaceum strains isolated from lisianthus in the USA. Diseased lisianthus plants spread throughout greenhouses even though several fungicides were applied. Additionally, they appeared from November to January and increased to 0.3% of the total number. Fusarium stem rot was found in 43.8% of the total number of farms from 2020-2021 in Okinawa Main Island.