RESISTANCE TO BELLY ROT IN CUCUMBER IDENTIFIED THROUGH FIELD AND DETACHED-FRUIT EVALUATIONS

Belly rot, caused by the fungal pathogen Rhizoctonia solani Kuhn,, is a severe disease in many regions that produce cucumber (Cucumis sativu s L.,), Annual crop loss to belly rot is commonly 5% to 10%, but losse s as high as 80% can occur in individual fields, There are no resistan t cultivars, so fungicides are used to provide partial control. Geneti c resistance in an acceptable cultivar would be more desirable and eco nomical, Studies were conducted in Summers 1991 and 1992 to screen pro mising germplasm for belly rot resistance using field and detached-fru it screening methods, In 1991, 105 cultigens (cultivars, breeding line s, and plant introduction accessions) were evaluated for belly rot res istance. The tests were repeated in 1992 with 63 cultigens, including the most resistant cultigens identified in 1991 and appropriate contro ls, Several cultigens were identified as potential sources of resistan ce genes. Pickling cucumbers showing resistance included PI 197085, PI 271328, and an F-4, selection of PI 197087 x PI 280096. Slicing cucum bers with resistance included 'Marketmore 76' and the F-1 of Gy 14 x P I 197087. Belly rot resistance was not correlated with other horticult ural traits measured, including fruit type, skin type, spine color, an d firmness. The resistant cultigens identified should be useful for de veloping cucumber cultivars with enhanced resistance to Rhizoctonia so lani.