We inoculate plants with the particular Phytophthora sojae race in the greenhouse. The respective disease reaction will be recorded seven days later. Standard soybean varieties with known reactions to selected races are included in the test. The exact races to be used will be determined with the client – depending on the Rps genes thought to be present. We get consistent results with races 1,7, 4, 20 and 25. Four replications with tens plants per variety are sown and inoculated for each race. The final report will include a summary indicating the type of resistance indicated by these tests (i.e., Rps 1c, 1k, 3 or 8 present) and whether segregation may still be occurring.
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.
Deploying one gene at a time can be a set up for failure because these single genes for resistance allow only those fungie that can defeat that gene to reporduce. This causes the original population of Phytophthora to change and results in a race between the fungus changing and breeders deploying new genes for resistance (of which we have few).
An alternative method of managing Phytophthora is to use field tolerance also known as partial resistance or field resistance. This is multigenic resistance that allows a ‘susceptible’ plant to grow in the presence of Phytophthora with little damage. We also screen for this type of resistance or tolerance.
Plants are sown into vermiculite over a layer of P. sojae race 25. Three weeks after planting plant roots are evaluated and rated. Plants will be compared in their reaction to soybean varieties of known partial resistance or tolerance. We use four replications twelve plants each in our standard test. Results are consistent with other reports.
Cost for this test will be $37.00 per variety entered.