Increase in Soybean Cyst Nematode Virulence and Reproduction on Resistant Soybean Varieties in Iowa From 2001 to 2015 and the Effects on Soybean Yields

Abstract

Management of the soybean cyst nematode (SCN) relies heavily on use of SCN-resistant soybean varieties to limit nematode reproduction and minimize yield loss. For Iowa, almost all SCN-resistant soybean varieties contain SCN resistance genes from a breeding line named Plant Introduction (PI) 88788. Iowa State University conducts experiments to evaluate numerous SCN-resistant and three to four SCN-susceptible soybean varieties in up to nine field experiments across Iowa each year. Data on SCN population density, virulence (SCN race and HG type), soybean yield, precipitation, and growing degree days from more than 25,000 four-row plots in field experiments conducted from 2001 to 2015 were analyzed to determine how these factors affected SCN reproduction and yield. SCN population densities were positively correlated with temperatures and negatively associated with precipitation during the growing seasons, indicating that SCN reproduction was greatest in hot, dry years. Over the years, virulence of SCN populations on PI 88788 increased in the fields in which the experiments were conducted, resulting in increased end-of-season SCN population densities and reduced yields of SCN-resistant soybean varieties with the PI 88788 source of resistance. These results indicate that soybean yield loss caused by SCN on resistant varieties with the common PI 88788 source of resistance likely will increase as virulence of SCN populations increases unless new sources of resistance become widely available and used in the future.

Therhg1-a(Rhg1low-copy) nematode resistance source harbors a copia-family retrotransposon within theRhg1-encoded α-SNAP gene

“…Rhg1 is the principal SCN-resistance locus in commercially grown soybeans. The increasing occurrence of SCN populations that at least partially overcome the overwhelmingly utilized "PI 88788type" rhg1-b resistance source is an important concern for soybean breeders and growers (McCarville, Marett, Mullaney, Gebhart, & Tylka, 2017), (www.thesc ncoal ition.com). Alternating use of different Rhg1 haplotypes should help bolster and preserve resistance against these virulent SCN populations (Brucker et al, 2005;Niblack et al, 2008)(www.thesc ncoal ition.com).…”

Biological control potential of plant growth‐promoting rhizobacteria suppression of Meloidogyne incognita on cotton and Heterodera glycines on soybean: A review

“…They found increasing population density, increase number of populations and increased yield loss over the 15 years. In the cases where PI 548402 source of resistance was used, this pattern was not seen (McCarville, Marett, Mullaney, Gebhart, & Tylka, ). New sources of resistance will be needed for the future.…”

Interactions of effects of host plant resistance and seed treatments on soybean aphid (Aphis glycines Matsumura) and soybean cyst nematode (Heterodera glycines Ichinohe)

“…Since the discovery of H. glycines in North America in 1954, management of this pest has relied on soybean germplasm with genetic resistance . Some of the main sources of H. glycines ‐resistant germplasm include Peking, PI88788, and PI90763, with PI88788 found in the vast majority of soybean cultivars that are currently labeled as resistant to H. glycines …”

“…Management of H. glycines with HPR has been complicated in recent years by the evolution of biotypes virulent to one of the most commonly used resistance genes, PI88788 . This trend likely resulted from farmers relying exclusively on a single form of HPR.…”

“…This trend likely resulted from farmers relying exclusively on a single form of HPR. For growers in the north‐central USA, >95% of the soybean cultivars with H. glycines resistance use the trait from PI88788 . Populations of H. glycines virulent to PI88788, according to the H. glycines HG type test, have been observed in Iowa, Illinois, Minnesota, Missouri and Ontario .…”