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.

No abstract

Reduction of linolenic acid content in soybean [Glycine max (L.) Merr.] oil is associated with improved odor and flavor characteristics. Germplasm with the lowest content of this fatty acid known in soybean (<25 g kg−1) was identified in 1986 at Iowa State University from the cross of two mutant lines, A5 × A23. The objective of our study was to determine the genetic control of the reduced linolenic acid content in two lines from that cross, AI6 and AfT. The two lines with < 25 g kg−1 linolenic acid were mated reciprocally to ‘Century 84’ (77 g kg−1 linolenic), the mutant line C1640 (37 kg−1 li nolenic) an d the parents, A5 and A23. There was no maternal effect when AI6 and AI7 were crossed to their parents, but a partial maternal effect was observed in crosses with Century 84 and C1640. In the crosses of Al6 and AI7 with Century 84, the segregation of the F2.3 lines satisfactorily fit a 1:14:1 ratio, which would be expected with the segregation of major genes at two independent loci. The data indicated that AI6 and AI7 obtained the fan(A5) allele from A5 and the fan2(A23) allele from A23. The continuous distributions observed in the AI6 and AI7 crosses with Century 84 indicated that minor genes and environmental effects also are important in the expression of linolenic acid content. Consequently, the low linolenic acid content of AI6 and AI7 can be considered a quantitative character for cultivar development programs.

that Race 3 SCN resistance in PI 88788 is inherited by three genes, with one recessive and two dominant. The Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is genetic evidence indicates that one of the dominant genes one of the most destructive soybean [Glycine max (L.) Merr.] pests is at a previously unreported locus which was designated worldwide. The most common source of SCN resistance used in soybean breeding in the northern USA is PI 88788. Previous research Rhg5 (Rao Arelli, 1994) the second gene is Rhg4, which has shown that PI 88788 carries a major quantitative trait locus (QTL) maps close to the i gene (Matson and Williams, 1965), conferring SCN resistance on linkage group (LG) G, which is believed and the recessive gene is rhg2. Genetic mapping efforts to be rhg1. The objective of our research was to map and confirm have since shown that PI 88788 has a major QTL on additional SCN resistance QTL in Bell, a cultivar with resistance LG G (Concibido et al., 1997), and a second minor QTL from PI 88788. One hundred four F 4 -derived lines (F 4 population) on LG C2 (Diers et al., 1997a). The QTL on LG G maps developed from crossing the cultivars Bell and Colfax were tested for to the same region where a major resistance locus was associations between 54 molecular markers and resistance to SCN mapped in PI 437654 (Webb et al., 1995), Peking, PI populations PA3 (HG type 7, race 3) and PA14 (HG type 1.3.5.6.7, 90763, PI 89772, and PI 209332 (Concibido et al., 1997; race 14). Three populations of near isogenic lines (NILs) were devel-Concibido et al., 1996; Yue et al., 2001). The resistance oped from F 4 plants heterozygous for a region on LG J where a significant QTL was identified in the F 4 population. The NIL popula-gene in this region has been designated rhg1 in the tions were tested with genetic markers and also for resistance to both literature and Cregan et al. (1999b) reported a linkage SCN populations. In the F 4 population, SCN resistance QTL were of 0.4 centimorgans (cM) between the simple sequence identified at both rhg1 and on LG J. The LG J QTL was confirmed repeat (SSR) marker Satt309 and rhg1 in crosses with in NIL populations and was given the confirmed QTL designation Peking and PI 209332 as sources of SCN resistance. cqSCN-003. The effect of cqSCN-003 was diminished in the NIL Although many QTL have been mapped in soybean, populations compared to the F 4 population. This was at least partially few have been confirmed in additional populations in the result of segregation distortion in the F 4 population between the the same or different genetic backgrounds. The confirregion containing rhg1 and the region containing cqSCN-003. These mation of QTL after initial mapping is a critical step results show the importance of verifying QTL in confirmation populabefore the selection of the QTL with markers in breedtions to estimate accurately their effects.ing programs. Near isogenic line populations are particularly useful for QTL confirmation because they are developed to segregate for QTL ...

Root and stem rot is one of the major diseases of soybean. It is caused by the oomycete pathogen Phytophthora sojae. A series of resistance genes (Rps) have been providing soybean with reasonable protection against this pathogen. Among these genes, Rps8, which confers resistance to most P. sojae isolates, recently has been mapped. However, the most closely linked molecular marker was mapped at about 10 cM from Rps8. In this investigation, we attempted to develop a high-density genetic map of the Rps8 region and identify closely linked SSR markers for marker-assisted selection of this invaluable gene. Bulk segregant analysis was conducted for the identification of SSR markers that are tightly linked to Rps8. Polymorphic SSR markers selected from the Rps8 region failed to show cosegregation with Phytophthora resistance. Subsequently, bulk segregant analysis of the whole soybean genome and mapping experiments revealed that the Rps8 gene maps closely to the disease resistance gene-rich Rps3 region.