A list of hundreds of SCN-resistant soybean varieties available for Iowa soybean farmers is compiled every fall as Iowa State University Extension and Outreach publication PM 1649, “Soybean cyst nematode-resistant soybean varieties for Iowa.” In addition to company, brand and variety name, the list includes information about each variety’s relative maturity, herbicide resistance traits, iron chlorosis tolerance, and genetic source of SCN resistance. The effort is supported by soybean checkoff funds from the Iowa Soybean Association.
There are 818 SCN-resistant soybean varieties included in the new list, which is fewer than in the past 8 years (see graph below). But there are varieties from 27 different brands included in this year’s publication, more than in recent years. Soybean cyst nematode graphic.
Number of SCN-resistant soybean varieties in maturity groups 0, 1, 2 and 3 for Iowa since 1991. Since 2006, almost 100% of varieties with “Other sources” have contained the Peking source of SCN resistance.
More choices of varieties with Peking SCN resistance for 2023 than in the past
Soybean varieties containing SCN resistance from the breeding line named Peking are highly valued. Currently in Iowa, Peking SCN resistance is more effective at limiting nematode reproduction and the buildup of SCN numbers in the soil than resistance from the PI 88788 breeding line, which is used in 95% of the varieties available to Iowa farmers. Yields of varieties with Peking SCN resistance frequently are greater than yields of varieties with PI 88788 SCN resistance because high levels of SCN reproduction on varieties with PI 88788 resistance cause significant yield suppression. ICM Newsletter articles here and here describe the situation in greater detail.
There are 47 varieties with SCN resistance from Peking in the updated publication, 13 more than in the 2021 list and the highest number of such varieties ever in the publication. Most (27) of the varieties with Peking SCN resistance are in maturity group 2. There are 16 varieties in maturity groups 0-1 with Peking resistance, and only 4 varieties are adapted for maturity group 3.
More varieties with Peking SCN resistance are needed
Reproduction of SCN populations present in Iowa fields on the PI 88788 source of resistance and resistant varieties developed with that breeding line has been increasing steadily since the early 2000s. The trend is not expected to subside. The low number of soybean varieties with Peking SCN resistance in maturity group 3 is particularly unfortunate because levels of reproduction of SCN populations on PI 88788 are among the highest in southern Iowa, as explained in a recent ICM News article.