Multi-pathogen disease caused by Didymella bryoniae and bacteriaon Styrian oil pumpkin: microbial ecology and biocontrol

Abstract: The Styrian oil pumpkin, Cucurbita pepo L. subsp. pepo var. styriaca Greb., is a cropof cultural, medical and commercial importance in Austria. Since 2004, fruit rot and black rotcaused by the ascomycete Didymella bryoniae (Fuckel) Rehm has lead to dramatic yield losses.In the field, the fungal disease was usually associated with characteristic symptoms ofbacteriosis. Bacterial pathogens included Pectobacterium carotovorum, Pseudomonas viridiflava,Pseudomonas syringae and Xanthomonas cucurbitae. The high coincidence of fungal andbacterial disease suggests mutualistic effects in pathogenesis. By cultivation-dependent methods,the fraction of Styrian oil pumpkin inhabiting in vitro antagonists against D. bryoniae andbacterial pathogens was investigated and ended in an ARDRA and BOX PCR based selection offive bacterial broad-spectrum antagonists from 2.320 initially tested microbes: strains ofLysobacter spp., Pseudomonas chlororaphis, Paenibacillus polymyxa and Serratia plymuthicawere the favorites. They were successfully evaluated in greenhouse and field trials. On theirbasis, a biological product to protect the Styrian oil pumpkin against microbial diseases will bedeveloped.