Optimization of the Heterodera glycines Race Test Procedure.

Effects of pot size, length of seedling radicle at the time of inoculation with Heterodera glycines, transplanting after inoculation, type and amount of inoculum, and temperature were tested to determine the optimum procedure for the H. glycines race test. Numbers of H. glycines females extracted from plants in 7.5-cm-d pots tended to be higher than numbers from 10-cm-d pots, but not significantly so. Radicle lengths from 2.5 cm to 7.5 cm had no effect. Transplanting after inoculation reduced the variation in the number of females extracted, but the numbers of females produced were very low. Plump females (40 per pot) or eggs (4,000 per pot) were the best inocula. A constant temperature of 28 C appeared to be optimum. More H. glycines females were extracted from plants 28 days after inoculation than at 35 days. Race tests in which all of these factors were included were still highly variable in the number of H. glycines females extracted from different replications of the same test host. Tests of several susceptible cultivars revealed differences in their capabilities as hosts of H. glycines races.