Performance and prospects of Rag genes for management of soybean aphid

Abstract

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an invasive insect pest of soybean [Glycine max (L.) Merr. (Fabaceae)] in North America, and it has led to extensive insecticide use in northern soybean-growing regions there. Host plant resistance is one potential alternative strategy for managing soybean aphid. Several Rag genes that show antibiosis and antixenosis to soybean aphid have been recently identified in soybean, and field-testing and commercial release of resistant soybean lines have followed. In this article, we review results of field tests with soybean lines containing Rag genes in North America, then present results from a coordinated regional test across several field sites in the north-central USA, and finally discuss prospects for use of Rag genes to manage soybean aphids. Field tests conducted independently at multiple sites showed that soybean aphid populations peaked in late summer on lines with Rag1 or Rag2 and reached economically injurious levels on susceptible lines, whereas lines with a pyramid of Rag1 + Rag2 held soybean aphid populations below economic levels. In the regional test, aphid populations were generally suppressed by lines containing one of the Rag genes. Aphids reached putative economic levels on Rag1 lines for some site years, but yield loss was moderated, indicating that Rag1 may confer tolerance to soybean aphid in addition to antibiosis and antixenosis. Moreover, no yield penalty has been found for lines with Rag1, Rag2, or pyramids. Results suggest that use of aphid-resistant soybean lines with Rag genes may be viable for managing soybean aphids. However, virulent biotypes of soybean aphid were identified before release of aphid-resistant soybean, and thus a strategy for optimal deployment of aphidresistant soybean is needed to ensure sustainability of this technology.

The Use of Refuge in Host Plant Resistance Systems for the Control of Virulent Biotype Adaptation in the Soybean Aphid (Hemiptera: Aphididae)

“…Field assessments have estimated percent virulence at Յ20% (Michel et al 2011, Wenger andMichel 2013), though, in a few instances, these Þeld populations have exceeded economic thresholds in single Rag varieties (Hesler et al 2013). A smaller virulent proportion in Þeld populations may decrease the likelihood of interbiotype competition in susceptible refuges, negating the ampliÞed Þtness advantage of biotype 3 (Donaldson et al 2007).…”

“…Thus, susceptible refuge plantings for HPR varieties could produce vastly different results than Bt IRM. Nonetheless, HPR varieties have proven effective in managing multiple pests (Smith and Clement 2012, Hesler et al 2013, Smith and Chuang 2014, and refuges are a plausible technique for increasing the durability and utility of current, and future, HPR varieties. Here we use growth chamber microcosms to investigate the use of susceptible refuges as method to limit the proliferation and adaptation of soybean aphid (Aphis glycines Matsumura) virulent biotypes.…”

“…Of these Þve, only Rag1 and Rag2 expressing varieties are available to growers, with both genes expressed individually or in combination (pyramid; Wiarda et al 2012, Hesler et al 2013. Though Rag1, Rag2, and their pyramid are successful in reducing aphid infestation (Hesler et al 2013), all three varieties have associated virulent biotypes (Table 1).…”

“…Of these Þve, only Rag1 and Rag2 expressing varieties are available to growers, with both genes expressed individually or in combination (pyramid; Wiarda et al 2012, Hesler et al 2013. Though Rag1, Rag2, and their pyramid are successful in reducing aphid infestation (Hesler et al 2013), all three varieties have associated virulent biotypes (Table 1). Virulent biotypes of the soybean aphid are believed to compose a minority of the current North American population (Hesler et al 2013), but virulence may proliferate rapidly, as Rag genes are more widely planted and place more intense selection pressure on aphid populations.…”

One Gene Versus Two: A Regional Study on the Efficacy of Single Gene Versus Pyramided Resistance for Soybean Aphid Management

“…At least three soybean aphid resistance genes have been identiÞed, with eight resistance genes proposed to date (Hill et al 2012, Hesler et al 2013). The Rag1 and Rag2 genes (both alone and together) appear to have no detrimental effects on agronomic performance (Kim and Diers 2009, Mardorf et al 2010, Brace and Fehr 2012.…”