Pseudomonas chlororaphis strain PA23 has consistently reduced stem rot of canola in greenhouse and field experiments.PCR analysis and Southern blotting detected the presence of phenazine and pyrrolnitrin biosynthetic genes in this bacterium. High performance liquid chromatography confirmed the production of phenazine, 2-hydroxy phenazine and pyrrolnitrin antibiotics.PA23 produces three organic volatiles (nonanal, benzothiozole, 2-ethyl, 1-hexanol) that are capable of completely inhibiting mycelial growth, and significantly reducing ascospore and sclerotia germination. Induction of higher activity of chitinase and β-1,3glucanase was observed, when the bacterium was challenge inoculated with the pathogen. Western blot analysis confirmed the induction of a 34 kDa chitinase protein. Transposon mutant PA23-314, which has a Tn5 insertion within the gacS gene, lacked antifungal activity in lab and greenhouse assays. Complementation with the wild-type gacS allele in trans restored antifungal activity, phenazine production, exoprotease, and N-acylhomoserine lactone to levels of the wild type. Another mutant PA23-63, a phenazine non-producer, mutated at the phzE gene of the phenazine biosynthetic operon, still produced pyrrolnitrin and exhibited antifungal activity suggesting that pyrrolnitrin could play a vital role in the antifungal activity of the bacterium. PA23 strain is capable of forming a biofilm that imparts resistance to lethal antibiotics. Strain PA23, a bacterium with several weapons in its armoury against Sclerotinia sclerotiorum, with the ability to grow as a biofilm is an excellent biological control agent for management of stem rot of canola.
W.G.Dilantha Fernando S.Nakkeeran T.de Kievit N.Poritsanos Y.Zhang T.C.Paulitz Z.Li R.Ramarathnam
Department of Plant Science, University of Manitoba, Winnipeg, MB Canada R3T 2N2 Department of Microbiology, Univedrsity of Manitoba, Winnipeg, MB Canada R3T 2N2 Department of Plant Pathology, Washington State University, Pullman, WA 99164-6430, USA Plant Protection Institute, Inner Mongolia Academy of Agricultural Sciences, Huhhot 010031, P.R.Chin