Abstract: Pseudomonas fluorescens FD6 strain produces several antifungal metabolites and inhibits mycelial growth of many plant pathogenic fungi. The partial sequence of sensor kinase gacS gene was PCR-amplified and used to construct a suicide vector pBS-S，which was introduced into strain FD6 to generate a gacS gene-insertion mutant FD6-MS by homologous recombinant. FD6-MS could not produce pyrrolnitrin，2,4-diacetylphloroglucinol，pyoluteorin，proteinase and HCN，and the siderphore production and biofilm formation were markedly reduced. The mutant FD6-MS failed to protect tomato fruits from grey mould caused by Botrytis cinerea HY2-1. The gacS complementary strain could restore the production of above antifungal compounds and protective effect against tomato grey mold. Our results suggest that the gacS gene in strain FD6 act as an important regulatory element in antibiotic production and disease suppression activity.

Key words: Pseudomonas fluorescens, gacS, antibiotics, Botrytis cinerea