Single plants are grown in cones and Phialophora gregata is injected into the base of 2-week-old plants. After five weeks, the progress of the fungus up the stem is determined by cutting the stem into one inch segments and incubating these sections on green bean agar. We record what portion of the stem has been colonized. We use Phialophora gregata genotype ‘A’ and a set of checks with known reactions. Girma Tabor et al describe this technique their article “Resistance to Phialophora gregata is expressed in the stems of resistant soybeans.”
Plant Disease 87: 970-976.
Cost for this test is $6.75 per replication. 10 replications are recommended.
If it is helpful to breeders we can maintain plant that appear resistant in these tests and take them to maturity in the greenhouse in order to harvest seed.