Number of SCN-resistant soybean cultivars in maturity groups 0, 1, 2, and 3 for Iowa since 1991. As of 2006, nearly 100 percent of “Other Source” cultivars contain the Beijing source of SCN resistance. (University of Iowa)
A list of hundreds of SCN-resistant soybean cultivars available to Iowa soybean growers is compiled each fall as Iowa State University Extension and Outreach Publication PM 1649, Soybean cyst nematode-resistant soybeanvaries for Iowa. In addition to company, brand, and variety names, the list includes information on each variety’s relative maturity, herbicide resistance traits, iron chlorosis tolerance, and genetic source of SCN resistance. The effort is supported by soybean settlement funds from the Iowa Soybean Association.
The new list contains 818 SCN-resistant soybean varieties, fewer than in the last eight years (see chart below). But there are strains from 27 different brands included in this year’s release, more than in previous years.
More selection of Peking SCN resistant strains for 2023 than in the past
Soybean varieties with SCN resistance from the Peking breeding line are highly valued. Currently, in Iowa, Peking SCN resistance is more effective in limiting nematode proliferation and accumulation of SCN numbers in soil than resistance from the PI 88788 strain line, used in 95% of the cultivars available to farmers in Iowa . Yields of Peking SCN-resistant cultivars are often higher than yields of PI 88788 SCN-resistant cultivars because high levels of SCN reproduction in PI 88788-resistant cultivars result in significant yield suppression. The ICM newsletter articles here and here describe the situation in more detail.
There are 47 SCN-resistant cultivars from Beijing in the updated publication, 13 more than in the 2021 list and the highest number of such cultivars ever included in the publication. Most (27) cultivars with Peking SCN resistance are in maturity group 2. There are 16 cultivars in maturity groups 0-1 with Peking resistance, and only 4 cultivars are adapted for maturity group 3.
More Peking SCN resistant varieties are needed
Reproduction of SCN populations found in Iowa fields on the PI 88788 resistance source and resistant cultivars developed using this breeding line has steadily increased since the early 2000s. The trend is not expected to slow down. The low number of Peking SCN-resistant soybean cultivars in maturity group 3 is particularly unfortunate since the reproductive rates of the SCN populations on PI 88788 are among the highest in southern Iowa, as explained in a recent ICM News article here becomes.