Control of Phytophthora cryptogea in the hydroponic forcing of witloof chicory with the rhamnolipid-based biosurfactant formulation PRO1

Abstract

Rhamnolipids, extracellular metabolites of Pseudomonas aeruginosa with surfactant properties, proved to be very effective in controlling the spread of brown root rot disease caused by Phytophthora cryptogea in the hydroponic forcing system of witloof chicory (Cichorium intybus var. foliosum). The biosurfactant was applied as the product PRO1, a formulation of 25% rhamnolipids in oil. Both an in vitro screening and in vivo experiments in a mini-hydroponic system demonstrated the ability of PRO1 to control brown root rot. A 25 μg mL-1 rhamnolipids nutrient solution was enough to obtain good control of an artificial infection with a zoospore suspension of P. cryptogea. The biosurfactant PRO1 performed well in a semicommercial system under growers' conditions. A treatment of 25 μg mL-1 rhamnolipids (100 μg mL-1 PRO1) reduced the disease incidence significantly in two independent experiments. However, PRO1 was not effective when a mycelial suspension was used as inoculum. Rhamnolipids have good potential to limit the spread of P. cryptogea in the hydroponic forcing system of witloof chicory, and can be used as a preventive measure against brown root rot. © 2005 BSPP.