Biological control of ornamental plant diseases caused by Fusarium oxysporum: A review

• Pathogenic Fusarium oxysporum are highly dangerous pathogens for ornamental production.
• Many microorganisms proved efficient in reducing diseases on ornamentals but too few are marketed.
• Known and new antimicrobial properties of botanicals may control pathogenic fungi of ornamentals.
• Biological control using microbes and botanicals is part of integrated disease management strategies.
• European legislation must change to encourage the marketing of products used in biological control.

Ornamentals include all decorative plants suitable for indoor or outdoor uses. A large variety of plants is produced and sold on a worldwide market. One of the most destructive pathogenic microorganisms for ornamental production is the soil-borne fungus Fusarium oxysporum. Many F. oxysporum pathogenic strains can infect numerous ornamental plants during production and/or post harvest storage. Once the disease has broken out, plants are rarely suitable for commercialization. No curative control method is currently available. The best management of the diseases can only be achieved through an integrative approach in which biological control can play a major role in complement of varietal selection for resistance, provided that lines are available, which is rarely the case. Biological control methods on ornamentals are limited to the use of microbial biological control agents and botanicals, i.e. essential oils or plant extracts. An overview of the studies about botanical and microorganism use against F. oxysporum on ornamentals highlighted that the use of these methods is less than 2 decades and that they arouse increasing interest. Microorganism and botanical sources are countless; consequently, the choice of a screening method to select good candidates is critical. Both microorganisms and botanicals display various modes of action that are not all fully understood, especially for botanicals. As soon as a promising microorganism or botanical candidate is identified, different parameters linked to the development of the product (mode of application, dose, formulation, production) need to be defined and standardized to optimize the quality of the final product. These steps also determine the success or failure of a product on the market. Once the product has been elaborated, the registration process can start. Depending on the country, requirements are different and the whole process is more or less tedious. However, 26 biological control products are currently available for F. oxysporum control on ornamentals, and the biological control market is growing. Moreover, biological control methods can be combined with one another or with other control methods but much additional research is required to develop methodologies for incorporating biologicals into other control strategies for ornamental disease management.