Stem rot of dwarf bean (Phaseolus vulgaris) caused by Sclerotinia sclerotiorum is a devastating disease worldwide, reducing the yield and quality of the bean crop. A fungal volatile organic compound (FVOC) produced by Trichoderma atroviride plays a major role in plant disease suppression. The ability of this FVOC when applied as a seed treatment to control S. sclerotiorum was investigated in a glasshouse pot experiment. S. sclerotiorum inoculum multiplied on sterile wheat-bran was added to 3-4 month potting mix at a rate of 0.5% w/w while non-inoculated potting mix was the no pathogen control. Seeds of dwarf bean cv. Messi were either left untreated (pathogen control and no pathogen control) or treated with the FVOC (75mM) applied in an inert polymer. For each of the three treatments five seeds were sown per pot with 12 replicates of each treatment. At 7 days after sowing (DAS) seedling emergence was 85% for the pathogen control but 97% for the no pathogen control and 98% for the FVOC treatment. By 28 DAS 10% of the plants in the pathogen control had died cf. none for the other two treatments, and by 68 DAS an additional 10% of the plants in the pathogen control were either dying or had died cf. none for the no pathogen control and 7% for the FVOC treatment. Disease progress (stem bleaching and immature sclerotia formation) in the pathogen control was rapid over this time but symptoms were mild in the FVOC treatment. Green pods were hand harvested 68 DAS (from eight of the twelve replicates). Compared to the pathogen control the FVOC treatment increased pod number by 63% and pod weight by 84%. Seeds were harvested from the remaining replicates at 112 DAS. The FVOC treatment increased seed yield by 260% over that of the pathogen control because of large and significant increases in seed number and 100-seed weight. Whether similar results can also be obtained in the field will now be investigated.

Key words: 6-pentyl-alpha-pyrone (6-PP), Sclerotinia sclerotiorum, seed coating, green bean yield, seed yield.