FIELD-TESTS FOR CUCUMBER RESISTANCE TO GUMMY STEM BLIGHT IN NORTH-CAROLINA

Gummy stem blight [Didymella bryoniae (Auersw.) Rehm] is the second mo st important pathogen of field-grown cucumbers (Cucumis sativus L.) in North Carolina and a severe problem for greenhouse-grown cucumbers wo rldwide. To determine whether resistance exists under North Carolina f ield conditions, 83 cultigens [cultivars, breeding lines, and plant in troduction (PI) accessions] were evaluated in the field for 4 years fo r their resistance to a mixture of D. bryoniae isolates. Plants were i noculated at the vine tip-over stage and rated for foliar lesion size and number. Cultigens identified as resistant in Wisconsin and The Net herlands were not resistant in North Carolina. When averaged over year s and locations, the most resistant C. sativus cultigens were PI 16443 3, 'Slice', PI 390264, M 17, and M 12. Several accessions of related C ucumis species were highly resistant: PI 299568 (C. myriocarpus Naud.) , PI 282450 (C. zeyheri Sond.), PI 299572 (C. myriocarpus), and PI 233 646 (C. anguria L.). The most susceptible cultivars were 'Colet', 'Mer esto', 'Supergreen', 'Dura', 'Pioneer', 'Marketmore 76', 'Pickmore', a nd 'Addis'. 'Calypso' and 'Dasher II', popular cultivars in North Caro lina, were moderately susceptible.