Gels of DNA amplification products from soybean plants with different susceptibility to frogeye leaf spot: a) marker CSOPA1800C in the PB cross, b) marker CSOPA21,250C in the PB cross, c) marker CSOUB11,100C in the UB cross. Lanes are as follows: 1, lambda phage DNA digested with EcoRI, BamHI and HindIII (size markers); 2, resistant cultivar; 3, susceptible cultivar; 4, resistant bulk; 5, susceptible bulk; 6-9, resistant F2 plants; and 10-11, susceptible plants. Arrows indicate the polymorphic DNA band.