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Modern soybean [Glycine max (L.) Merr.] breeding extensively uses as crossing parents superior cultivars and breeding lines with locally adapted desirable traits, which may lead to declined genetic diversity and increased frequency of fixed common alleles. The main objective of this research was to evaluate, via amplified fragment length polymorphism (AFLP) markers, the genetic diversity and the genetic relationships among the 38 most popular cultivars and lines in the southern United States. Genetic analysis using AFLP markers with 16 primer combinations revealed an average genetic distance of 0.124 among the 38 genotypes examined. Genetic diversity declined among cultivars released during the 1950s and 1960s compared to those released before the 1950s, but increased in the 1970s and peaked in the 1980s, followed by a decline again in the 1990s and 2000s. While 34 unique bands were identified, allelic frequency analysis revealed 50.8% of the 754 loci examined to be fixed in all 38 genotypes. Future parent selection for crossing should consider using genotypes of greater genetic distance and avoid using lines with common genetic background. [ABSTRACT FROM AUTHOR]

A quantitative trait locus (QTL) for waterlogging tolerance has been identified in a northern cultivarArcher. In the current study, Archer was crossed with two southern elite soybean cultivars A5403 and P9641 to investigate the efficiency of marker-assisted selection and phenotypic selection for waterlogging tolerance and to assess the value of waterlogging tolerance for soybean yield improvement. Near-isogenic lines (NILs) were created using the linked simple sequence repeat (SSR) marker Sat_064 for the waterlogging tolerance QTL from each of the F6-derived populations. Concurrently, 103 and 67 recombinant inbred lines (RILs) were also generated from Archer x A5403 and Archer x P9641, respectively. Significant variations in seed yield or plant injury were observed among the NILs and RILs under waterlogging stress. The 29 most tolerant and 29 most sensitive NILs and RILs were selected on the basis of waterlogging injury ratings and evaluated under irrigated and waterlogged conditions in Arkansas and Missouri in 2002 and 2003. The most tolerant lines produced an average of 60.9% of their irrigated yield, as compared with only 32.6% and 53.9% by the most sensitive lines and the commercial checks, respectively. Waterlogging injury scores for the tolerant lines, checks, and sensitive lines were 3.6, 4.3, and 6.6, respectively, following the same trend as their yield reductions. A genotype-by-environment interaction (G x E) analysis showed that some of the selected lines were highly stable in response to waterlogging stress across environments. Breeding selection for the waterlogging tolerance can be performed in the field based on seed yield and plant injury scores. [ABSTRACT FROM PUBLISHER]

Soil water-logging can cause severe damage to soybean [ Glycine max (L.) Merr.] and results in significant yield reduction. The objective of this study was to identify quantitative trait loci (QTL) that condition water-logging tolerance (WLT) in soybean. Two populations with 103 and 67 F6:11 recombinant inbred lines (RILs) from A5403 × Archer (Population 1) and P9641 × Archer (Population 2), respectively, were used as the mapping populations. The populations were evaluated for WLT in manually flooded fields in 2001, 2002, and 2003. Significant variation was observed for WLT among the lines in the two populations. No transgressive tolerant segregants were observed in either population. Broad-sense heritability of WLT for populations 1 and 2 were 0.59 and 0.43, respectively. The tolerant and sensitive RILs from each population were selected to create a tolerant bulk and a sensitive bulk, respectively. The two bulks and the parents of each population were tested with 912 simple sequence repeat (SSR) markers to select candidate regions on the linkage map that were associated with WLT. Markers from the candidate regions were used to genotype the RILs in both populations. Both single marker analysis (SMA) and composite interval mapping (CIM) were used to identify QTL for WLT. Seventeen markers in Population 1 and 15 markers in Population 2 were significantly ( p <0.0001) associated with WLT in SMA. Many of these markers were linked to Rps genes or QTL conferring resistance to Phytophthora sojae Kaufmann and Gerdemann. Five markers, Satt599 on linkage group (LG) A1, Satt160, Satt269, and Satt252 on LG F, and Satt485 on LG N, were significant ( p <0.0001) for WLT in both populations. With CIM, a WLT QTL was found close to the marker Satt385 on LG A1 in Population 1 in 2003. This QTL explained 10% of the phenotypic variation and the allele that increased WLT came from Archer. In Population 2 in 2002, a WLT QTL was located near the marker Satt269 on LG F. This QTL explained 16% of the phenotypic variation and the allele that increased WLT also came from Archer. [ABSTRACT FROM AUTHOR]

Water-saturated soils and flooding (submergence) can greatly reduce soybean [Glycine max (L.) Merr.] yield. Mapping analyses with the simple sequence repeat (SSR) marker Sat_064 have identified a quantitative trait locus (QTL) for tolerance to waterlogging in the cultivar Archer. Our objectives were to evaluate the effect of this QTL on waterlogging tolerance in southern environments and genetic backgrounds, and to assess variability for waterlogging tolerance in Archer derived populations. We used Sat_064 genotype data to create seven sets of NILs from the populations A5403 × Archer and 9641 × Archer. The NILs were grown under waterlogged (water level 70-120 mm above the soil surface for 2 wk starting at flowering) and irrigated control conditions at three environments in 1999 and 2000 and evaluated each for yield and visual waterlogging injury. Waterlogging injury was rated on a 0 (no symptoms) to 9 (>90% severely chlorotic or dead) scale. Checks and select RILs from the same crosses were also tested. Additional RILs from each population were tested for waterlogging injury in 2000. The Sat_064 marker did not account for a significant portion of the variability among the NILs for either waterlogging tolerance based on yield, yield in waterlogged conditions, or waterlogging injury. This may be due to the southern genetic backgrounds and environments in this study as the Sat_064 QTL was originally identified in northern genetic backgrounds and environments. Variation for waterlogging tolerance and waterlogging injury was noted in the RIL populations. The most tolerant RILs suffered a 32% yield reduction from waterlogging and had a waterlogging injury rating of 1.3 while the most susceptible RILs suffered a 77% yield loss and had a waterlogging injury score of 6.8. The populations segregated for waterlogging tolerance independently of the Sat_064 marker. Visual assessment of waterlogging injury was associated with yield-based assessment of waterlogging tolerance and could be used to select for lines with improved waterlogging tolerance. [ABSTRACT FROM AUTHOR]