W1 Locus Research Articles

β-diketone accumulation in response to drought stress is weakened in modern bread wheat varieties (Triticum aestivum L.).

Cuticular waxes coating leaf surfaces can help plants tolerate drought events by reducing non-stomatal water loss. Despite their role in drought tolerance, little is known about how cuticular wax composition has changed during breeding in Canadian bread wheat (Triticum aestivum L.) varieties. To fill in this gap, flag leaves of the Canadian Heritage Bread Wheat Panel, which include 30 varieties released between 1842 and 2018, were surveyed to determine if and how cuticular wax composition in wheat has changed at two breeding ecozones over this period. Following this, a subset of varieties was subjected to drought conditions to compare their responses. As expected, modern varieties outperformed old varieties with a significantly larger head length and reaching maturity earlier. Yet, when challenged with drought, old varieties were able to significantly increase the accumulation of β-diketones to a higher extent than modern varieties. Furthermore, RNAseq was performed on the flag leaf of four modern varieties to identify potential markers that could be used for selection of higher accumulation of cuticular waxes. This analysis revealed that the W1 locus is a good candidate for selecting higher accumulation of β-diketones. These findings indicate that the variation in cuticular waxes upon drought could be further incorporated in breeding of future bread wheat varieties.

A Novel Pinkish-White Flower Color Variant Is Caused by a New Allele of Flower Color Gene W1 in Wild Soybean (Glycine soja)

The enzyme flavonoid 3′,5′-hydroxylase (F3′5′H) plays an important role in producing anthocyanin pigments in soybean. Loss of function of the W1 locus encoding F3′5′H always produces white flowers. However, few color variations have been reported in wild soybean. In the present study, we isolated a new color variant of wild soybean accession (IT261811) with pinkish-white flowers. We found that the flower’s pinkish-white color is caused by w1-s3, a single recessive allele of W1. The SNP detected in the mutant caused amino acid substitution (A304S) in a highly conserved SRS4 domain of F3′5′H proteins. On the basis of the results of the protein variation effect analyzer (PROVEAN) tool, we suggest that this mutation may lead to hypofunctional F3′5′H activity rather than non-functional activity, which thereby results in its pinkish-white color.

Refining the genetic architecture of flag leaf glaucousness in wheat

Key messageThe cuticle is the plant’s barrier against abiotic and biotic stresses, and the deposition of epicuticular wax crystals results in the scattering of light, an effect termed glaucousness. Here, we dissect the genetic architecture of flag leaf glaucousness in wheat toward a future targeted design of the cuticle.The cuticle serves as a barrier that protects plants against abiotic and biotic stresses. Differences in cuticle composition can be detected by the scattering of light on epicuticular wax crystals, which causes a phenotype termed glaucousness. In this study, we dissected the genetic architecture of flag leaf glaucousness in a panel of 1106 wheat cultivars of global origin. We observed a large genotypic variation, but the geographic pattern suggests that other wax layer characteristics besides glaucousness may be important in conferring tolerance to abiotic stresses such as heat and drought. Genome-wide association mapping identified two major quantitative trait loci (QTL) on chromosomes 3A and 2B. The latter corresponds to the W1 locus, but further characterization revealed that it is likely to contain additional QTL. The same holds true for the major QTL on 3A, which was also found to show an epistatic interaction with another locus located a few centiMorgan distal to it. Genome-wide prediction and the identification of a few additional putative QTL revealed that small-effect QTL also contribute to the trait. Collectively, our results illustrate the complexity of the genetic control of flag leaf glaucousness, with additive effects and epistasis, and lay the foundation for the cloning of the underlying genes toward a more targeted design of the cuticle by plant breeding.

Molecular Genetic Analysis of a Novel Recessive White Flower Gene in Wild Soybean

Cultivated soybean [Glycine max (L.) Merr.] flowers are either white or purple, whereas nearly all wild soybean (G. soja Sieb. and Zucc.) accessions have purple flowers. As a result, the soybean flower color phenotype has attracted the attention of plant breeders, biochemists, and population geneticists. Here, we report genetic mapping of a novel recessive white flower gene in YWS415, a wild soybean accession collected in Korea. The W1 locus, which is the major locus determining purple (W1) or white (w1) flower color, encodes flavonoid 3′ 5′‐hydroxylase in YWS415, which was more similar to the common W1‐type sequences than w1‐type sequences. Subsequent mapping results using an F2 population from a cross between the ‘Hwangkeum’ (purple flower) and YWS415 variants indicated that the white flower color was controlled by a recessive allele at the W4 locus that encodes dihydroflavonol‐4‐reductase 2 (DFR2). The w4 allele arose through insertion of a 5584‐bp nonautonomous transposon member of soybean GM_CACTA_33 family into the second intron of DFR2. It was designated as GM_CACTA_33_w4. Results from this study will enhance our understanding of soybean white flower inheritance and facilitate marker‐assisted selection for the antioxidative anthocyanins in soybeans.

Identification and Molecular Analysis of Four New Alleles at the W1 Locus Associated with Flower Color in Soybean.

In soybean, flavonoid 3′5′-hydroxylase (F3′5′H) and dihydroflavonol-4-reductase (DFR) play a crucial role in the production of anthocyanin pigments. Loss-of-function of the W1 locus, which encodes the former, or W3 and W4, which encode the latter, always produces white flowers. In this study, we searched for new genetic components responsible for the production of white flowers in soybean and isolated four white-flowered mutant lines, i.e., two Glycine soja accessions (CW12700 and CW13381) and two EMS-induced mutants of Glycine max (PE1837 and PE636). F3′5′H expression in CW12700, PE1837, and PE636 was normal, whereas that in CW13381 was aberrant and missing the third exon. Sequence analysis of F3′5′H of CW13381 revealed the presence of an indel (~90-bp AT-repeat) in the second intron. In addition, the F3′5′H of CW12700, PE1837, and PE636 harbored unique single-nucleotide substitutions. The single nucleotide polymorphisms resulted in substitutions of amino acid residues located in or near the SRS4 domain of F3′5′H, which is essential for substrate recognition. 3D structure modeling of F3′5′H indicated that the substitutions could interfere with an interaction between the substrate and heme group and compromise the conformation of the active site of F3′5′H. Recombination analysis revealed a tight correlation between all of the mutant alleles at the W1 locus and white flower color. On the basis of the characterization of the new mutant alleles, we discussed the biological implications of F3′5′H and DFR in the determination of flower colors in soybean.

Analysis of anthocyanin pigments in soybean hypocotyl

The T and W1 loci determine color and anthocyanin content in soybean hypocotyls. In purple hypocotyls, the anthocyanins were: A1, a delphinidin-type anthocyanin; A2 made of two unresolved peaks: peonidin 3,5-di-O-glucoside and a delphinidin-type anthocyanin; and A3, accounting for >90% of the total, was malvidin 3,5-di-O-glucoside. A single peak, peonidin 3,5-di-O-glucoside, was observed in the bronze hypocotyls.

A Metabolic Gene Cluster in the Wheat W1 and the Barley Cer-cqu Loci Determines β-Diketone Biosynthesis and Glaucousness.

The glaucous appearance of wheat (Triticum aestivum) and barley (Hordeum vulgare) plants, that is the light bluish-gray look of flag leaf, stem, and spike surfaces, results from deposition of cuticular β-diketone wax on their surfaces; this phenotype is associated with high yield, especially under drought conditions. Despite extensive genetic and biochemical characterization, the molecular genetic basis underlying the biosynthesis of β-diketones remains unclear. Here, we discovered that the wheat W1 locus contains a metabolic gene cluster mediating β-diketone biosynthesis. The cluster comprises genes encoding proteins of several families including type-III polyketide synthases, hydrolases, and cytochrome P450s related to known fatty acid hydroxylases. The cluster region was identified in both genetic and physical maps of glaucous and glossy tetraploid wheat, demonstrating entirely different haplotypes in these accessions. Complementary evidence obtained through gene silencing in planta and heterologous expression in bacteria supports a model for a β-diketone biosynthesis pathway involving members of these three protein families. Mutations in homologous genes were identified in the barley eceriferum mutants defective in β-diketone biosynthesis, demonstrating a gene cluster also in the β-diketone biosynthesis Cer-cqu locus in barley. Hence, our findings open new opportunities to breed major cereal crops for surface features that impact yield and stress response.

Wide genetic variation in phenolic compound content of seed coats among black soybean cultivars.

Black soybeans have been used as a food source and also in traditional medicine because their seed coats contain natural phenolic compounds such as proanthocyanidin and anthocyanin. The objective of this research is to reveal the genetic variation in the phenolic compound contents (PCCs) of seed coats in 227 black soybean cultivars, most of which were Japanese landraces and cultivars. Total phenolics were extracted from seed coats using an acidic acetone reagent and the proanthocyanidin content, monomeric anthocyanin content, total flavonoids content, total phenolics content, and radical scavenging activity were measured. The cultivars showed wide genetic variation in PCCs. Each of the contents was highly correlated with one another, and was closely associated with radical scavenging activity. PCCs were also moderately associated by flowering date but not associated by seed weight. Cultivars with purple flowers had a tendency to produce higher PCCs compared with cultivars with white flowers, suggesting that the W1 locus for flower color can affect phenolic compound composition and content. Our results suggest that developing black soybean cultivars with high functional phenolic compounds activity is feasible.

Allele-specific marker development and selection efficiencies for both flavonoid 3′-hydroxylase and flavonoid 3′,5′-hydroxylase genes in soybean subgenus soja

Color is one of the phenotypic markers mostly used to study soybean (Glycine max L. Merr.) genetic, molecular and biochemical processes. Two P450-dependent mono-oxygenases, flavonoid 3′-hydroxylase (F3′H; EC1.14.3.21) and flavonoid 3′,5′-hydroxylase (F3′5′H, EC1.14.13.88), both catalyzing the hydroxylation of the B-ring in flavonoids, play an important role in coloration. Previous studies showed that the T locus was a gene encoding F3′H and the W1 locus co-segregated with a gene encoding F3′5′H in soybean. These two genetic loci have identified to control seed coat, flower and pubescence colors. However, the allelic distributions of both F3′H and F3′5′H genes in soybean were unknown. In this study, three novel alleles were identified (two of four alleles for GmF3′H and one of three alleles for GmF3′5′H). A set of gene-tagged markers was developed and verified based on the sequence diversity of all seven alleles. Furthermore, the markers were used to analyze soybean accessions including 170 cultivated soybeans (G. max) from a mini core collection and 102 wild soybeans (G. soja). For both F3′H and F3′5′H, the marker selection efficiencies for pubescence color and flower color were determined. The results showed that one GmF3′H allele explained 92.2 % of the variation in tawny and two gmf3′h alleles explained 63.8 % of the variation in gray pubescence colors. In addition, two GmF3′5′H alleles and one gmF3′5′h allele explained 94.0 % of the variation in purple and 75.3 % in white flowers, respectively. By the combination of the two loci, seed coat color was determined. In total, 90.9 % of accessions possessing both the gmf3′h-b and gmf3′5′h alleles had yellow seed coats. Therefore, seed coat colors are controlled by more than two loci.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-013-2063-3) contains supplementary material, which is available to authorized users.

An Active CACTA-Family Transposable Element is Responsible for Flower Variegation in Wild SoybeanGlycine soja

A plant producing flowers with purple and white variegation was discovered in an accession of G. soja that was introduced from Russia. The mutant line was designated as B00146-m. Lines with white flowers (B00146-w) and purple flowers (B00146-r) were developed from the progeny of B00146-m. The flower color was controlled by the W1 locus encoding a flavonoid 3’5’-hydroxylase (F3’5’H). The allele for variegated flowers was designated as w1-m. The gene symbol was approved by the Soybean Genetics Committee. PCR suggested that a DNA fragment with a molecular size of ≈3.9 kb was inserted in the first exon of the F3’5’H gene in B00146-m, whereas such insertion was not observed in B00146-w and B00146-r. These results suggested that an active mobile element was inserted in the first exon and was responsible for flower variegation. The inserted fragment was identified as a 3883 bp long CACTA-family transposable element and it was designated as Tgs1. Similarity of overall sequence and terminal inverted repeats suggested that Tgs1 and the soybean lectin gene transposable element Tgm1 comprise a subgroup. Frequency of germinal reversion was low probably due to the integration into an exon. Tgs1 had a truncated version of the transposase gene and may be a nonautonomous element. The Plant Genome: Published ahead of print 29 Mar. 2012; doi: 10.3835/plantgenome2011.11.0028

A new allele of flower color gene W1 encoding flavonoid 3'5'-hydroxylase is responsible for light purple flowers in wild soybean Glycine soja

BackgroundGlycine soja is a wild relative of soybean that has purple flowers. No flower color variant of Glycine soja has been found in the natural habitat.ResultsB09121, an accession with light purple flowers, was discovered in southern Japan. Genetic analysis revealed that the gene responsible for the light purple flowers was allelic to the W1 locus encoding flavonoid 3'5'-hydroxylase (F3'5'H). The new allele was designated as w1-lp. The dominance relationship of the locus was W1 >w1-lp >w1. One F2 plant and four F3 plants with purple flowers were generated in the cross between B09121 and a Clark near-isogenic line with w1 allele. Flower petals of B09121 contained lower amounts of four major anthocyanins (malvidin 3,5-di-O-glucoside, petunidin 3,5-di-O-glucoside, delphinidin 3,5-di-O-glucoside and delphinidin 3-O-glucoside) common in purple flowers and contained small amounts of the 5'-unsubstituted versions of the above anthocyanins, peonidin 3,5-di-O-glucoside, cyanidin 3,5-di-O-glucoside and cyanidin 3-O-glucoside, suggesting that F3'5'H activity was reduced and flavonoid 3'-hydroxylase activity was increased. F3'5'H cDNAs were cloned from Clark and B09121 by RT-PCR. The cDNA of B09121 had a unique base substitution resulting in the substitution of valine with methionine at amino acid position 210. The base substitution was ascertained by dCAPS analysis. The polymorphism associated with the dCAPS markers co-segregated with flower color in the F2 population. F3 progeny test, and dCAPS and indel analyses suggested that the plants with purple flowers might be due to intragenic recombination and that the 65 bp insertion responsible for gene dysfunction might have been eliminated in such plants.ConclusionsB09121 may be the first example of a flower color variant found in nature. The light purple flower was controlled by a new allele of the W1 locus encoding F3'5'H. The flower petals contained unique anthocyanins not found in soybean and G. soja. B09121 may be a useful tool for studies of the structural and functional properties of F3'5'H genes as well as investigations on the role of flower color in relation to adaptation of G. soja to natural habitats.

A Rearrangement Resulting in Small Tandem Repeats in the F3′5′H Gene of White Flower Genotypes Is Associated with the Soybean W1 Locus

Soybean [Glycine max (L.) Merr.] flower pigmentation is controlled by six loci, W1, W2, W3, W4, Wm, and Wp, of which the functions of only three are known. None of the recessive alleles at those three loci completely abolishes flower pigmentation. On the other hand, the W1 locus is required for flower pigmentation. Based on genetic and biochemical data, the trihydroxylation reaction to form delphinidin‐3‐glucoside has been postulated as a likely function of the W1 locus. We report the cloning and sequencing of a flavonoid 3′5′‐hydroxylase (F3′5′H) gene from the purple flower soybean line L79‐908 (W1) and the recessive allele from the white flower isoline ‘Williams’ (w1). The mutation is a rearrangement leading to a small (65 bp) insertion of tandem repeats in exon 3 that truncates the translation product prematurely. The presence of this insertion in all‐white flower soybean lines examined and in those of a segregating population resulting from a cross between purple and white flower lines presents compelling evidence that the F3′5′H gene isolated is likely encoded by the W1 locus of Glycine max. GmF3′5′H is a single‐copy gene, expressed at very low levels in all tissues examined, including flower and seed coats, but sufficient to account for the contribution of the delphinidin‐based anthocyanins and/or proanthocyanins in these tissues.

Evaluation of insect-mediated seed set among soybean lines segregating for male sterility at the ms6 locus

Currently, there is no economical way to produce large quantities of F 1 hybrid soybean seed in the USA. One of the fundamental requirements for hybrid seed production is the availability of a stable male-sterile, female-fertile system. However, the more challenging barrier is the efficient transfer of pollen from the male parent to the female parent. This could potentially be achieved through pollinator insects. Our observations suggested that seed set on male-sterile, female-fertile plants is a good indicator of insect attraction. The objective of this study was to evaluate seed set among male-sterile, female-fertile lines segregating for male-sterile, female-fertile ms6 allele by using Megachile rotundata as pollinator vector. Thirty-four pairs of near-isogenic lines, the ms6 w1w1 donor parent, and its two isogenic lines W1w1 and w1w1 segregating for male-sterile ( ms6) allele were used. The W1 locus controls flower color and hypocotyle pigmentation. Seed set was evaluated on field-grown plants in 2001–2003 near Ames, IA. Although the observed seed set was not commercially acceptable, our results indicated significant differences in seed set among lines. This suggests that preferential attraction of pollinators occurred, and selection among male-sterile, female-fertile lines could be used to obtain female parents suitable to produce larger amounts of hybrid soybean seed. In addition, the effect of flower color on seed set was statistically significant. White-flowered lines ( w1w1) produced more seed set compared to purple-flowered lines ( W1W1). Lastly, the important effect of year suggested that the effect of environmental conditions on seed set among lines segregating for male sterility was of paramount importance to plant–pollinator interactions. This needs to be assessed in order to establish an efficient hybrid soybean program.

The Pd2 and Lf2 Loci Define Soybean Linkage Group 16

Despite progress made in constructing the molecular map of soybean [Glycine max (L.) Merr.], many genes remain to be located on the classical map. The genetic linkage studies reported here were undertaken to advance the construction of the classical genetic map. Hybridizations were made in the field and the F2 and F3 generations were produced and classified in the greenhouse or field at Beltsville, MD. Data were tested by chi‐square for single‐factor segregation and linkage. Recombination estimates were made by the maximum likelihood method. The Lf2 locus (controlling leaflet number) segregated independently of the T, Ln, W1, Rj1, F, Y17, Df4, Fr2, and Pc loci. The Pd2 locus (controlling pubescence density) segregated independently of the W1 locus. The chi‐square for Lf2 and Pd2 strongly indicated linkage. The recombination frequency between the Lf2 and Pd2 loci was estimated at 12 ± 2.2%. Soybean breeders attempting to couple or decouple the Lf2 and Pd2 alleles in their breeding populations should take cognizance of this linkage association in estimating the population sizes required to achieve their goals.

Production of near-isogenic lines of common wheat for glaucousness and genetic basis of this trait clarified by their use.

Duplication of the genes for both wax production (W loci) and inhibition (proposed symbol, Iw loci) on chromosomes 2B and 2D hindered clarification of the allelic and linkage relationships between these loci in wheat. The near-isogenic lines of three genotypes, w1w1 w2w2, W1W1 w2w2 and w1w1 W2W2, for wax production (all iw1iw1 iw2 iw2 for wax inhibition) and two genotypes, Iw1Iw1 iw2 iw2 and iw1 iw1 Iw2Iw2, for wax inhibition (both W1W1 W2W2 for wax production) therefore were produced by ten backcrosses with Triticum aestivum cv. S615 (genotype W1W1 W2W2 iw1iw1 iw2iw2), or its equivalent w-S615 (w1w1 w2w2 iw1iw1 iw2iw2), as the recurrent parent. Segregation ratios between glaucous and non-glaucous plants in successive backcross generations or after selfing the backcrossed offspring indicated that all the wax-producing (W) and inhibiting (Iw) alleles were transmitted at equal frequencies to their respective recessive alleles, w and iw. Linkage analyses of W1, Iw1 and Ne2 (a gene for hybrid necrosis) on chromosome 2B and W2, Iw2 and C (a gene for compact ear) on chromosome 2D showed that the W1 and W2 loci respectively are located at sites different from the Iw1 and Iw2 loci. The presently accepted concept of multiple allelism for w, W and WI (wax inhibition) therefore is invalid. Rather two allelic sets, w and W, and iw and Iw, both of which are duplicated on chromosomes 2B and 2D, must be postulated for the glaucousness of wheat. The first genetic maps showing their linkage relationships to the centromere and the Ne2 and C loci have been constructed.

Recombination Values for the Ms6‐W1 Chromosome Region in Different Genetic Backgrounds in Soybean

Recombination values in plants are influenced by genetic factors, environmental conditions, and their interactions. In soybean, Glycine max (L.) Merr., the cosegregation method to produce hybrid seed depends on the close linkage of the Ms6(pollen fertility) locus and the W1 (flower color) locus. Twenty-four near-isogenic lines, cosegregating at the Ms6 and W1 loci, (Ms6W1 ms6w1 ), were developed with the ms6-w1 donor cytoplasm and the recurrent parent cytoplasms. The objectives were to determine the recombination values between the Ms6 and W1 loci from both testcross and F2-family data. The recombination value for the Ms6 and W1 loci from the testcross data in the ms6-w1 donor cytoplasm was 3.14 ± 0.80 and in the recurrent parent cytoplasms was 3.62 ± 0.89. From the F2- family data, the recombination value for the Ms6 and W1 loci in the ms6-w1 donor cytoplasm was 3.06 ± 0.35 and in the recurrent parent cytoplasms was 4.90 ± 0.35. The recombination values for the F2-family data were statistically significantly different (P = 0.05) for the ms6-w1 donor cytoplasm versus the recurrent parent cytoplasms. However, the recombination values are acceptable to continue to use the cosegregation method to produce hybrid soybean seed.

Genetics and cytology of a new genic male-sterile soybean [ Glycine max (L.) Merr.

Genetic and cytological studies were conducted with a new male-sterile, female-fertile soybean [Glycine max (L.) Merr.] mutant. This mutant was completely male sterile and was inherited as a single-recessive gene. No differences in female or male gamete transmission of the recessive allele were observed between reciprocal cross-pollinations in the F1 or F2 generations. This mutant was not allelic to any previously identified soybean genic male-sterile mutants: ms1, ms2, ms3, ms4, ms5, or ms6. No linkage was detected between sterility and flower color (W1 locus), or between sterility and pubescence color (T1 locus). Light microscopic and cytological observations of microsporogenesis in fertile and sterile anthers were conducted. The structure of microspore mother cells (MMC) in male-sterile plants was identical to the MMCs in male-fertile plants. Enzyme extraction analyses showed that there was no callase activity in male-sterile anthers, and this suggests that sterility was caused by retention of the callose walls, which normally are degraded around tetrads at the late tetrad stage. The tapetum from male-sterile anthers also showed abnormalities at the tetrad stage and later stages, which were expressed by an unusual formation of vacuoles, and by accumulation of densely staining material. At maturity, anthers from sterile plants were devoid of pollen grains.

Hybrid Soybean Seed Production: Comparison of Three Methods

Improved methods to produce hybrid soybean [Glycine max (L.) Merr.] seed could augment several types of research. Two previously described methods, the traditional method and the dilution method, require insect‐facilitated cross‐pollination of ms ms nuclear male‐sterile plants. The traditional method requires a substantial time investment during flowering to remove fertile siblings, and the dilution method requires a substantial amount of land and pollen‐parent seed. Because time, land, and seed are limited, a more efficient method would be valuable. The cosegregation method was developed, utilizing close genetic linkage between the W1 locus and the Ms6 locus. The W1 ___, seedling has a purple hypocotyl; the w1 w1 seedling has a green hypocotyl. The ms6 ms6 plant is male sterile and female fertile. Approximately 97% of the purple‐hypocotyl seedlings, W1 ___, in a line segregating for the w1 and ms6 alleles in coupling phase will he fertile, Ms6 ___, and can be removed as a pollen source at the first‐trifoliolate stage. Our objective was to evaluate and compare the three methods of hybrid soybean seed production for seed yield, efficiency, and hybrid seed purity and quality. We used a randomized complete‐block design (three replications per location, three locations, two years). The cosegregation method gave higher seed yield, better efficiency, and equal or better seed quality (percentage germination, 100‐seed weight) than the other methods. Male‐sterile plants yielded an average of 28.6 seeds plant−1 with the cosegregation method, 18.2 seeds plant−1 with the traditional method, and 9.5 seeds plant−1 with the dilution method. The cosegregation method will be useful in several research areas, including genetic control of complex traits, prediction of parental value, recurrent selection, and commercialization of hybrid soybean.

Genetic allelism and linkage tests of a soybean gene, Rfg1, controlling nodulation with Rhizobium fredii strain USDA 205

A soybean gene, Rfg1, controlling nodulation with strain USDA 205, the type strain for the fast-growing species Rhizobium fredii, was tested for allelism with the Rj4 gene. The Rj4 gene conditions ineffective nodulation primarily with certain strains of the slow-growing soybean microsymbiont, Bradyrhizobium elkanii. The F2 seeds of the cross of the cultivars Peking, carrying the alleles rfg1, Rj4, i (controlling inhibition of seed coat color) and W1 (controlling flower color), and Kent, carrying the alleles Rfg1, rj4, i-i and w1, were evaluated for nodulation response with strain USDA 205 by planting surface disinfested seeds in sterilized vermiculite in growth trays and inoculating with a stationary phase broth culture of strain USDA 205 at planting. Plants were classified for nodulation response visually after four weeks growth and transplanted to the field for F3 seed production. Flower color, purple (W1) vs white (w1), was determined in the field. The allele present at the i locus was determined by classification of F3 seed coat color. The F3 seeds were planted in growth trays and inoculated with strain USDA 61 of Bradyrhizobium elkanii to determine the genotype for the Rj4 locus. The Rfg1 and Rj4 genes were determined to be located at separate loci. Chi-square analysis for linkage indicated that Rfg1 segregated independently of the Rj4, I and W1 loci.

Inheritance of Pink Flower in Soybean

In soybean [Glycine max (L.) Merr.], there are several possible flower colors: white, near‐white, purple, purple‐throat, and magenta. We report a new flower color, described as pink, which is distinct from all previously reported flower colors. Segregation ratios for the progeny row in which the mutant was found, and subsequent selfed progeny, indicate that the pink flower color is controlled by a single recessive gene. When this pink‐flowered plant was crossed with all reported flower color genes and the F2 populations classified for flower color, results indicate that the pink flower gene is independent of known flower color genes and acts as a modifier gene to decrease pigment expression at the W1 locus. We propose the gene symbol wp to be used to describe pink flower color inheritance.