staining. However, these visualization methods require either expensive or hazardous radioactive chemicals and Microsatellite DNA markers are widely used in genetic research.are time-consuming. Electrophoresis with MetaPhor Their use, however, can be costly and throughput is sometimes limited. The objective of this paper is to introduce a simple, low-cost, high-agarose gels (Cambrex Corporation, East Rutherford, throughput system that detects amplification products from microsa-NJ) has been used to separate alleles of microsatellite tellite markers by nondenaturing polyacrylamide gel electrophoresis. markers, but the resolution is lower than nondenaturingThis system is capable of separating DNA fragments that differ by polyacrylamide gels and the cost is currently five times as little as two base pairs. The electrophoresis unit holds two vertical more than that of nondenaturing polyacrylamide gels. 100-sample gels allowing standards and samples from a 96-well plateCapillary electrophoresis also has been used to deterto be analyzed on a single gel. DNA samples are stained during mine length polymorphisms of microsatellite markers electrophoresis by ethidium bromide in the running buffer. In addi- (Marino et al., 1995), but this method requires sophistition, one of the gel plates is UV-transparent so that gels can be cated instruments and fluorescently tagged primers, photographed immediately after electrophoresis without disassemwhich are expensive. Here we describe an inexpensive bling the gel-plate sandwich. Electrophoresis runs are generally less than two hours. The cost per gel, excluding PCR cost, is currently and relatively high-throughput system developed for the estimated at about $2.60, or less than $0.03 per data point. This system purpose of genotyping with microsatellite markers. has been used successfully with soybean [Glycine max (L.) Merr.] and wheat (Triticum aestivum L.) microsatellite markers and could 1828

Glycine soja, the wild progenitor of soybean, is a potential source of useful genetic variation in soybean improvement. The objective of our study was to map quantitative trait loci (QTL) from G. soja that could improve the crop. Five populations of BC(2)F(4)-derived lines were developed using the Glycine max cultivar IA2008 as a recurrent parent and the G. soja plant introduction (PI) 468916 as a donor parent. There were between 57 and 112 BC(2)F(4)-derived lines in each population and a total of 468 lines for the five populations. The lines were evaluated with simple sequence repeat markers and in field tests for yield, maturity, plant height, and lodging. The field testing was done over 2 years and at two locations each year. Marker data were analyzed for linkage and combined with field data to identify QTL. Using an experimentwise significance threshold of P=0.05, four yield QTL were identified across environments on linkage groups C2, E, K, and M. For these yield QTL, the IA2008 marker allele was associated with significantly greater yield than the marker allele from G. soja. In addition, one lodging QTL, four maturity QTL, and five QTL for plant height were identified across environments. Of the 14 QTL identified, eight mapped to regions where QTL with similar effects were previously mapped. Many regions carrying the yield QTL were also significant for other traits, such as plant height and lodging. When the significance threshold was reduced and the data were analyzed with simple linear regression, four QTL with a positive allele for yield from G. soja were mapped. One epistatic interaction between two genetic regions was identified for yield using an experimentwise significance threshold of P=0.05. Additional research is needed to establish whether multiple trait associations are the result of pleiotropy or genetic linkage and to retest QTL with a positive effect from G. soja.

Round soybean seeds are sought-after for food-type soybean. Also the genetic control of seed geometry is of scientific interest. The objectives of this study were to estimate heritability and map quantitative trait loci (QTLs) responsible for seed shape traits. Three densely mapped recombinant inbred populations each with 192 segregants were used, Minsoy x Archer, Minsoy x Noir1, and Noir1 x Archer. A two rep two location experiment was conducted in Los Andes, Chile, and East Lansing, MI, USA. Seed height (SH), width (SW), length (SL), and seed volume (SV) as width x height x length were measured to determine seed shape. Heritability was estimated by variance component analysis. A total of 19 significant QTLs (LOD >or= 3.7) in ten linkage groups (LG) were detected for all the traits. Only one QTL was stable across populations and environments and six were stable in at least two populations in both environments. The amount of phenotypic variation explained by a single QTL varied from 7.5% for SH, to 18.5% for SW and at least 30% of the genetic variation for the traits is controlled by four QTL or less. All traits were highly correlated with each other in all populations with values ranging from 0.5 to 0.9, except for SL and SW that were not significantly correlated or had a low correlation in all populations. Narrow sense heritabilities for all traits ranged from 0.42 to 0.88. We note that LG u9, u11, and u14 are hot points of the genome for QTLs for various traits. The number and genomic distribution of the QTLs confirms the complex genetic control of seed shape. Transgressive segregation was observed for all traits suggesting that careful selection of parents with similar phenotypes but different genotypes using molecular markers can result in desirable transgressive segregants.

A linkage mapping approach was used to identify quantitative trait loci (QTL) associated with day-neutrality in the commercial strawberry, Fragaria · ananassa (Duch ex Rozier). Amplified Fragment Length Polymorphism (AFLP) markers were used to build a genetic map with a population of 127 lines developed by crossing the dayneutral (DN) ÔTributeÕ with the short-day (SD) ÔHoneoyeÕ. The population was genotyped with AFLP markers and 429 single dose restriction fragments (SDRF) were placed on a consensus map of 1541 cM with 43 linkage groups. Individuals from the mapping population were observed for their flowering habit throughout the growing season in Michigan (MI), Minnesota (MN), Maryland (MD), Oregon (OR) and California (CA). Eight QTL were found that were either location specific or shared among locations. None of these QTL explained >36% of the phenotypic variation, indicating that the inheritance of day-neutrality is likely a polygenic trait.Two primary types of commercial strawberries are grown, short-day (SD) and day-neutral (DN). SD genotypes or Junebearers, initiate flower buds either under SD conditions (<14 h of day length) or at temperatures below 15°C, while DN genotypes are photoperiod insensitive and will initiate flowers under any photoperiod conditions as long as temperatures are moderate (Darrow 1966, Hancock 1999. Dayneutrality was most recently introduced into modern cultivars by Bringhurst and Voth (1984), using a native genotype of F. virginiana (Mill) ssp. glauca (S. Watson) Staudt from the Wasatch Mountains of Utah.To date, the genetics of day-neutrality in strawberries have remained elusive. Several different models have been proposed including: (i) regulation by a single dominant gene Voth 1978, Ahmadi et al. 1990); (ii) regulation by dominant complementary genes (Ourecky and Slate 1967); and (iii) quantitative inheritance (Powers 1954, Hancock et al. 2001). The reason why these studies generated different hypotheses may be that they utilized different sets of parents and were conducted in different environments. The study of Ourecky and Slate (1967) was conducted in New York using material that had not recently had any new F. virginiana germplasm incorporated. The studies of Powers (1954) and Hancock et al. (2001), were performed in Wyoming and Michigan, respectively, using DN parents that carried genes from F. · ananassa and wild clones of F. virginiana that were different from the Wasatch source. The studies of Bringhurst and Voth (1978) and Ahmadi et al. (1990) were performed in CA using University of California-Davis breeding parents carrying the Wasatch source of day-neutrality. There was one study in CA that suggested day-neutrality may have a quantitative basis (Shaw 2003), but it was later refuted by a more extensive statistical analysis of a greater number of progeny populations (Shaw and Famula 2005). Sugimoto et al. (2005) found a RAPD-marker linked to a dominant gene regulating day-neutrality in a Japanese breeding population carrying the Wasatch source of day-neutrality.To e...

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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 ...

Several greenhouse inoculation methods are available to evaluate soybean (Glycine max (L.) Merr.) for resistance to Sclerotinia sclerotiorum (Lib.) de Bary. Most of these methods are labor intensive and often produce inconsistent results among the tests. The objective of this research was to develop a low-cost and high-efficiency greenhouse inoculation method that can generate a consistent result. We developed a spray-mycelium method in which mycelia were cultured in liquid potato dextrose broth and homogenized before spraying on the soybean leaves. We also developed an inoculation method (the “drop-mycelium” method) in which a drop of homogenized mycelium suspension was dropped on the tips of main stems. Inoculated plants were incubated in a greenhouse chamber with 60 to 80% relative humidity. Plant mortality and area under the wilt progress curve (AUWPC) were used to measure disease severity daily from 3 to 14 days after inoculation (DAI). Eighteen soybean genotypes, including partially resistant line NKS19-90 and susceptible line Resnik, were employed in this study. The spray-mycelium method and the drop-mycelium method were compared with the cut-petiole method in the greenhouse. The three experiments were a randomized complete block design. Twenty-four plants per genotype in each experiment were inoculated at V3 growth stage in the greenhouse. Significant differences (P < 0.05) in disease ratings of plant mortality and AUWPC to Sclerotinia stem rot were found among 18 tested genotypes. The results obtained with the spray-mycelium and drop-mycelium inoculation methods were significantly (R > 0.73, P <0.01) correlated with the results obtained with the cut-petiole inoculation method for both of the plant mortality and AUWPC. Compared with the cut-petiole method, the spray-mycelium and the drop-mycelium methods used less inoculation time and are less expensive in terms of materials. Both of these new methods are low cost, efficient, and reliable and they can be valuable for large-scale evaluation of germ plasm and breeding lines for resistance to Sclerotinia stem rot in a greenhouse or other similar facilities.

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