Screening the cucumber germplasm collection for resistance to gummy stem blight in North Carolina field tests

Gummy stem blight (Didymella blight), caused by Didymella bryoniae (Auersw, ) Rehm and its anamorph Phoma cucurbitacearum (Fr.:Fr.) Sacc., is the secon d most important disease of cucumber (Cucumis sativus L,) in North Carolina after root knot nematodes Meloidogyne sp, Both Didymella blight and Phoma blight, caused by Phoma exigua Desm, have similar symptoms and control prac tices, and are generally referred to as gummy stem blight,In order to deter mine whether resistance existed to North Carolina isolates of D. bryoniae, 851 cultigens [cultivars, breeding lines, and plant introduction (PI) lines ] were evaluated in the field. Plants were inoculated with one selected iso late (highly pathogenic in preliminary greenhouse tests) at the vine tip-ov er stage. They were rated for foliage lesion size and number on a 0 to 9 vi sual scale (0 = no disease, 9 = plant killed) and average ratings for 10 pl ants per plot were analyzed. The ratings ranged from 2.0 (highly resistant) to 8.5 (highly susceptible) with a mean of 6.2. The most resistant breedin g lines and PI accessions were PI 200815, PI 390243, 'LJ 90430', PI 279469, and PI 432855, The most resistant cultivars were 'Homegreen #2', 'Little J ohn', 'Transamerica', and 'Poinsett 76', The most susceptible cultigens in the study were PI 288238, PI 357843, PI 357865, and PI 167134, Two popular cultivars in North Carolina,'Calypso' and 'Dasher II', were moderately resi stant.