Stem rot of dwarf bean caused by Sclerotinia sclerotiorum is a devastating disease worldwide, reducing the yield and quality of the bean crop. The fungal volatile organic compound 6-pentyl-alpha-pyrone (6-PP) plays a major role in plant disease suppression. The ability of 6-PP 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 6-PP (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 6-PP 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 6-PP treatment. Disease progress (stem bleaching and immature sclerotia formation) in the pathogen control was rapid over this time but symptoms were mild in the 6-PP treatment. Green pods were hand harvested 68 DAS (from eight of the twelve replicates). Compared to the pathogen control the 6-PP treatment increased pod number by 63% and pod weight by 84%. Seeds were harvested from the remaining replicates at 112 DAS. 6-PP 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.