Producing cellâfree culture broth of rhamnolipids as a costâeffective fungicide against plant pathogens
2012
Sha, Ruyi | Jiang, Lifang | Meng, Qin | Zhang, Guoliang | Song, Zhirong
Biosurfactants of rhamnolipids have been enthusiastically investigated for substitutes of synthetic agrochemicals against plant pathogens. However, all such studies have been conducted on rhamnolipids with high purity which have limitations due to high costs. This paper focused on the applicability of rhamnolipidâcontaining cellâfree culture broth. It was found that rhamnolipids in cellâfree culture broth of Pseudomonas aeruginosa ZJU211 were largely composed of diârhamnolipid and monoârhamnolipid with the ratio varying with culture time. After 96 h of fermentation, the mass ratio of diârhamnolipid over monoârhamnolipid increased to 2.6:1. Crude rhamnolipids in a form of cellâfree culture broth showed high antifungal activity against colony growth and biomass accumulation of seven plant pathogens comprising two Oomycetes, three Ascomycota and two Mucor spp. fungi, among which three plant pathogens were firstly reported in this paper showing inhibition to rhamnolipids. Particularly, rhamnolipids showed potent activity against two Oomycetes that acquire resistance to commercial compound of metalaxyal. Furthermore, diârhamnolipid was elucidated to dominate the antifungal activity of crude rhamnolipids by in vitro studies. At last, the efficacy and safety of cellâfree culture broth was preliminarily illustrated on plants in vivo. So cellâfree culture broth as a crude rhamnolipid product could be served as a potential costâeffective and environmentalâfriendly fungicide in agriculture. (© 2012 WILEYâVCH Verlag GmbH & Co. KGaA, Weinheim)
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