The effect of accelerated seed ageing on cucumber germination following seed treatment with fungicides and microbial biocontrol agents for managing gummy stem blight by Didymella bryoniae

This study examined (1) the effect of the accelerated seed ageing on cucumber germination with treatments: Bacillus subtilis QST713 or Pseudomonas fluorescens CA in 1% methylcellulose and fungicides difenoconazole, carboxin or pyraclostrobin in 5% polyvinyl alcohol, and (2) the impact on disease severity of gummy stem blight (GSB) caused by Didymella bryoniae by the seed treatments and foliar spray application of methylcellulose-formulated B. subtilis or P. fluorescens. Difenoconazole, pyraclostrobin and microorganisms suppressed growth of D. bryoniae in a laboratory dual culture; carboxin had no effect on D. bryoniae growth. Germination of fungicide-treated seed was unaffected by accelerated seed ageing. Greenhouse: GSB disease severity with PVA and non-treated seed was 89% and 84%, respectively, whereas, difenoconazole, carboxin and pyraclostrobin, was significantly reduced, 56%, 53% and 40%, respectively. Germination of Bacillus-treated seed was unaffected by accelerated seed ageing, but was significantly reduced with Pseudomonas-treated seed. GSB disease severity with B. subtilis or P. fluorescens-treated seed was inconsistent; however, foliar spray application of B. subtilis significantly reduced GSB. Accelerated seed ageing exposed a significant negative impact on seed germination with P. fluorescens. Based on the accelerated ageing test, P. fluorescens-treated cucumber seed is detrimental to seed survival and therefore, is not a candidate for biocontrol activities for cucumber requiring seed storage.