Soybean Cyst Nematode Virulence to PI 88788 Soybean Resistance in Iowa: Selection Marches Steadily On

Management of the soybean cyst nematode (SCN) in Iowa has relied on resistant soybean varieties derived largely from a single resistance breeding line, namely PI 88788. A 2017 summary of results of Iowa State University SCN-resistant variety trial experiments from 2001-2015 revealed sustained reliance on PI 88788-derived resistant varieties was associated with increased SCN virulence to PI 88788 resistance and negative effects on yield. Recently, we added eight additional years of data and repeated the analyses to determine if trends and conclusions reported for 2001-2015 continued through 2023. And indeed, the major trends persisted. Virulence to PI 88788 increased at a rate nearly identical to that predicted in 2017 and resulted in increasing yield loss from SCN on varieties possessing PI 88788 resistance. Linear regression analyses now predict that by the end of this decade, varieties with PI 88788 resistance will provide only approximately 40% control of SCN, resulting in average losses of roughly 9 bu/acre or 12% yield potential. Although no significant increase in SCN reproduction on varieties with Peking (PI 548402) resistance was detected, there were more experiments with elevated (>10%) SCN reproduction on Peking resistance from 2016-2023 than in experiments conducted from 2001-2015. Our data illustrate immediate action by the soybean industry is needed to increase availability of varieties with PI 88788 and with Peking sources of SCN resistance. Also, rapid farmer implementation of a balanced SCN management approach using soybean varieties with different sources of resistance is imperative to mitigate expected and predictable increased yield losses.