High-Resolution Mapping of the Region around the Soybean Virus Resistance Genes, Rsv1 and Rpv1
Gore, Michael Allen
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Soybean mosaic virus (SMV) and peanut mottle virus (PMV) are potyviruses that can cause serious yield reductions in soybean [Glycine max (L.) Merr.]. Virus resistant soybean cultivars have been released with alleles at the Rsv1 and Rpv1 locus that confer resistance to SMV and PMV, respectively. A high-resolution map-based cloning approach was undertaken to isolate Rsv1 and Rpv1 from soybean, with hopes of providing insight into this host-pathogen relationship. A mapping population of 1,056 F2 individuals was constructed from the cross of the resistant cultivar PI 96983 (Rsv1 and Rpv1) by the susceptible cultivar Lee 68 (rsv1 and rpv1). Ninety-one of the 1,056 F2 individuals had a cross-over (recombination) in the chromosomal region between microsatellite, or simple sequence repeat (SSR) marker loci Hsp176 and Sat120, and these 91 recombinant lines (RLs) were selected for further genetic analysis. Genotypes of Rsv1 and Rpv1 for the 91 RLs were obtained by inoculating their F2:3 progeny with SMV-G1 and PMV-P1, respectively. The 91 RLs also were used for mapping one random amplified polymorphic DNA (RAPD), five SSR, and 21 restriction fragment length polymorphism (RFLP) markers. Included in these RFLP markers were seven resistance gene candidate (RGC) and five resistance gene candidate flanking (RGCF) markers. RGC probes encode a protein with homology to previously cloned plant disease resistance genes, and RGCF probes are sequences obtained from the flanking regions of candidate disease resistance genes. The resultant high-resolution map consisted of 41 marker loci detected by 27 molecular markers. Rsv1 and Rpv1 cosegregated with one or more RFLP bands detected by RGCF probes: GG27-1a, 3gG2SP, and/or T3G. Analyses of the disease reaction and molecular marker data from seven RLs suggested that the map position of Rsv1 should be at a locus different from that designated by the linkage analysis software, Mapmaker 3.0. Compared to the other 89 RLs, a high percentage (>34%) of F3 plants grown from four of these seven RLs gave a necrotic reaction when inoculated with SMV-G1. From this evidence, we believed that another locus independent of Rsv1 was involved in PI 96983's response to SMV-G1. The two loci conferring resistance to SMV-G1 were designated Rsv1a and Rsv1b.
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