Abstract: Effects of biosurfactants on plant fungal diseases have been received much attention worldwide. Rhamnolipid is an anionic biosurfactant synthesized by Pseudomonas aeruginosa, with great potential as an inhibitor of plant pathogenic fungi. However, the comprehensive evaluation on its antifungal spectrum and antifungal activity is not fully explored. In this study, 29 common plant’s pathogenic fungi were collected. The sensitivity of pathogenic fungi at different taxonomic levels to the inhibition of rhamnolipid was evaluated based on Ainsworth fungal systemic taxonomy. The results showed that the inhibition effect of rhamnolipid on Oomycotawas the best. When the concentration of crude extraction of rhamnolipid was 0.3 g·L^-1, the inhibition rate for Pythium attrantheridium, Pythium irregular, and Pythium acanthicum mycelium was 80%, followed by Deuteromycota. When the concentration was 0.5g·L^-1, the inhibition rate for Verticillium dahliaeand Rhizoctonia solani reached higher than 80%. However, the effect of rhamnolipid was poor, even not effective to inhibit Ascomycetes andZygomycetes of pathogenic fungi. Furthermore, the observation of the morphological structure of fungal hyphae showed that rhamnolipid destroyed the cell wall of fungal mycelium and changed the permeability of cell membrane, and thus inhibited the growth of mycelium. As far as our knowledge, this study is the first one to show that rhamnolipid could inhibit the growth of Fusarium proliferatumand Fusarium redolens. The inhibition rate of rhamnolipid against hyphae was 63% and 74%, respectively, when the crude extraction of rhamnolipid was 1.0 g·L^-1. This study comprehensively evaluated the antifungal spectrum and ability of rhamnolipid from taxonomic status of pathogenic fungi, which provided technical support for the development of biological control technology of plant’s pathogenic fungi.

Key words: rhamnolipid, plant pathogenic fungi, antifungal effect, biocontrol.