Abstract
Soybeans (G. max) infected with F. oxysporum yielded up to 59% less than uninfected controls in field studies at Georgetown and Newark, Delaware [USA]. Of 10 cultivars tested, ''York'' was among the more resistant and gave the highest percentage of uninoculated yield at both locations. Resistance to F. oxysporum was detected using greenhouse screening techniques, and a rapid test tube screening method was developed that determined resistance levels in 16 days. Cultivars resistant to F. oxysporum were also detected using a mycelium production index. This new method is not destructive and permits saying resistant plants for use in a breeding program.