Inhibition of Fungi from Diseased Grape by Syringomycin E-Rhamnolipid Mixture

Abstract

Fungal infections of vineyard grapes compromise the yield and sensory properties of wines. Consequently, there is a need for more effective fungal control measures. The aim of this work was to evaluate the potential of a novel lipopeptide fungicidal formulation to control these diseases. A mixture of rhamnolipids (RLs) and the lipodepsinonapeptide syringomycin E (SRE) showed greater inhibitory activities than SRE alone against fungi isolated from grape berries and stems of a heavily infected vineyard in Louisiana. The fungal species tested were <i>Aspergillus japonicus, Cladosporium cladosporioides</i>, <i>Curvularia brachyspora</i>, <i>Greeneria uvicola, Nigrospora sphaerica, Trichoderma</i> sp., <i>Penicillium sclerotiorum,</i> and <i>P. thomii</i>. Exposure to SRE resulted in 50% killing of germinating conidia of all these fungal species at concentrations between 0.75 and 3 μM and the SRE + RL mixture gave 50% killing between 0.75 and 1 μM SRE. Nongerminated conidia of only <i>C. brachyspora</i> were killed by SRE alone or SRE + RLs (both giving 50% killing at &lt;1 μM SRE). The RLs alone did not affect the growth of either germinating or nongerminating conidia of these fungi. Results demonstrate the potent and broad fungicidal properties of SRE and show that when mixed with RLs, it is even more lethal to a wide range of grape-associated fungi in the germination stage.