Prevalence of soil-borne diseases in Kalanchoe blossfeldiana reveals a complex of pathogenic and opportunistic fungi

Greenhouse cultivation of ornamentals is subjected to a high incidence of soil-borne fungal pathogens. In Kalanchoe, these pathogens are responsible for root and stem rot, and for infection of the vascular tissue. Well-known soil-borne pathogens are believed to cause these diseases. Yet, a systematized survey of these pathogens is lacking for Kalanchoe produced commercially. Here, we studied the occurrence of soil-borne fungal pathogens associated with cultivation of Kalanchoe in Denmark and production of cuttings and stock plants in greenhouse facilities located in Turkey and Vietnam. Molecular identification of pathogens complemented mycological identification and pathogenicity testing of the soil-borne fungal pathogens. This study revealed that the fungi Corynespora cassiicola, Thielaviopsis basicola, Fusarium solani, and F. oxysporum are the most prevalent pathogens associated with root and stem rotting and wilt of Kalanchoe under the conditions studied. Furthermore, the study showed that some of the pathogens are part of an infection complex comprising both primary and opportunistic fungal species. The fact that some of the pathogens were present in some regions, while absent in others, suggests how they move between greenhouse facilities on infected plant material. This study generated important information about the soil-borne fungal complex affecting Kalanchoe, which is useful for a better understanding of the biology of the disease and for designing control strategies.