Biological control of Sclerotinia sclerotiorum (Lib.) de Bary, the causal agent of white mold, by Pseudomonas species on canola petals.

Sclerotinia sclerotiorum is an important pathogen on canola. Due to the public concern over pesticide use, alternative methods of disease control, such as biological control, should be considered. Several bacterial strains were isolated from canola and soja plants. Inhibition of S. sclerotiorum by bacterial strains in vitro was assayed on PDA medium in dual culture test. Eight Pseudomonas sp. strains (PB-3, PB-4, PB-5, PB-6, PB-7, PB-8, PB-10 and PB-11) caused inhibition zone against 5. sclerotiorum hyphal growth. The biocontrol potential of the bacteria was tested in a plant assay. Disease suppression was investigated using a petal inoculation technique. Canola petals were pretreated with bacteria, and then inoculated with 5. sclerotiorum ascospores 24 h later. Greenhouse experiment showed that application of Pseudomonas sp. strains (1 x 10(8) cfu ml(-1)) effectively suppressed S. sclerotiorum (1 x 10(5) ascospores ml(-1)) on petals and all of them achieved significant (P<0.01) disease suppression. Fourteen days after inoculation, strain PB-3 had 88/7% disease control and strain PB-4 had 69/9% disease control. Result from all studies indicates PB-3 to be effective biocontrol against S. sclerotiorum of canola. PB-3, PB-4, PB-7, PB-8, PB-10 and PB-11 were identified as Pseudomonas fluorescens biovar III. PB-5 and PB-6 was identified as Pseudomonas fluorescens biovar II. Strains PB-3, PB-4, PB-6, PB-10 and PB-11 produced protease and HCN. Strain PB-5 produce protease; no HCN.