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

specific chromosome regions (Mock, 1972). The discordant results found by different investigators for the same Recombination values in plants are influenced by genetic factors, chromosome region may be attributed to genotype 3 environmental conditions, and their interactions. In soybean, Glycine environment interaction, chromosome structure differmax (L.) Merr., the cosegregation method to produce hybrid seed depends on the close linkage of the Ms6(pollen fertility) locus and ences between the parents (Stephens, 1950), and which the W1 (flower color) locus. Twenty-four near-isogenic lines, coseparent was the male or the female parent (Rhoades, gregating at the Ms6 and W1 loci, (Ms6W1 ms6w1 ), were developed 1941; Burt et al., 1991; Williams et al., 1995). Extensive with the ms6-w1 donor cytoplasm and the recurrent parent cytodata show significant differences in recombination valplasms. The objectives were to determine the recombination values ues obtained from coupling data as opposed to repulsion between the Ms6 and W1 loci from both testcross and F2-family data, or backcross (testcross) data as opposed to F2 data data. The recombination value for the Ms6 and W1 loci from the (Mather, 1951; Butler, 1968). In addition, controls and testcross data in the ms6-w1 donor cytoplasm was 3.14 6 0.80 and treatments must be replicated adequately so that chance in the recurrent parent cytoplasms was 3.62 6 0.89. From the F2extreme values will not be attributed to treatments (Butfamily data, the recombination value for the Ms6 and W1 loci in ler, 1977). the ms6-w1 donor cytoplasm was 3.06 6 0.35 and in the recurrent parent cytoplasms was 4.90 6 0.35. The recombination values for the In soybean, the pollen fertility locus, Ms6, is linked F2-family data were statistically significantly different (P 5 0.05) for to flower color locus, W1 (Palmer and Skorupska, 1990). the ms6-w1 donor cytoplasm versus the recurrent parent cytoplasms. Cross-pollinations of genetic types T295 (ms6 ms6) 3 However, the recombination values are acceptable to continue to use ‘Calland’, and Calland 3 T295H (Ms6 ms6), and T295 3 the cosegregation method to produce hybrid soybean seed. ‘Cutler’ and 3 ‘Hark’ gave recombination values for Ms6-W1 between 2.48 6 0.1 and 3.18 6 0.1 (Skorupska and Palmer, 1989). Lewers and Palmer (1993), by using R values vary in plants as do many three different Linkage Group 8 genetic stocks, reported other phenotypes. Intrinsic and extrinsic factors recombination values for Ms6-W1 between 3.86 6 0.69 affecting recombination may be random or directed for and 4.78 6 1.46. All seven genetic combinations were in coupling phase and indicated close linkage of the two loci. R.G. Palmer, USDA ARS CICGR and Dep. of Agronomy and of The cosegregation of the ms6 and w1 alleles has been Zoology/Genetics, Iowa State Univ., Ames, IA 50011; J.B. Holland, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011; K.S. Lewers, used to produce large quantities of hybrid soybean seed Dep. of Agronomy, Iowa State Univ., Ames, IA 50011. Joint contribu(Lewers et al., 1996). The W1_ seedlings have purple tion of the Iowa Agric. and Home Economics Exp. Stn, Ames, IA, hypocotyls and purple flowers; w1 w1 seedlings have J. Paper No. J-17361, project no. 3352, and the USDA ARS CICGR. green hypocotyls and white flowers. The ms6 ms6 plants The mention of a trademark or proprietary product does not constitute are male sterile and female fertile. Approximately 97% a guarantee or warranty of the product by Iowa State Univ. or the USDA and does not imply its approval to the exclusion of other of the purple-hypocotyl seedlings, W1_, in a family segproducts that may be suitable. Received 20 May 1997. *Corresponding regating for the w1 and ms6 alleles in coupling phase author ([email protected]). will be fertile plants, Ms6_. More than 92% of the greenhypocotyl seedlings are expected to be male-sterile (ms6 Published in Crop Sci. 38:293–296 (1998). 294 CROP SCIENCE, VOL. 38, MARCH–APRIL 1998 Table 1. Soybean cultivars, breeding lines, and plant introductions used to generate Ms6 ms6 backcross-derived lines. Public lines Private lines Ancestral lines Plant introductions BSR 101 AGO20 Asgrow Seed Co. A.K. (Harrow)† China Century AX2858 Asgrow Seed Co. Manchu PI 91167† Corsoy 79 A3307† Asgrow Seed Co. Mandarin PI 261474† Elgin CX-155 DeKalb Genetics Corp. Mandarin (Ottawa) PI 427099† Hack† 82-165† Land O’Lakes, Inc. Richland Hardin 82-378† Land O’Lakes, Inc. Japan Hoyt J-201 Mycogen Seeds PI 297544† G3917 Novartis Seeds, Inc. PI 370059 S1346 Novartis Seeds, Inc. PI 384474 P422-57 Pioneer Hi-Bred, Int’l. P596-13 Pioneer Hi-Bred, Int’l. USSR P3010-02 Pioneer Hi-Bred, Int’l. PI 227333† Glenn ProfiSeed, Inc. PI 416941 PI 417076 † These lines or plant introductions are white flower (w1w1 ), other lines or plant introductions are purple flower (W1W1 ). are high-yielding accessions introduced into the USA, five ms6) plants. Either phenotype can be identified and lines are important ancestors of modern soybean cultivars, removed at the first trifoliolate stage. seven are important public cultivars, and 13 are private comPalmer and Lewers (1998) have developed 68 nearpany cultivars or breeding lines. The pedigree of the ms6-w1 isogenic lines segregating at the Ms6 locus. These neardonor cytoplasm is Hawkeye/Lincoln/2/Grant/3/Amsoy 71/4/ isogenic lines were developed from ancestral, public, Bonus/Cutler (Palmer and Skorupska, 1990). The procedure and private company breeding lines as recurrent parused to backcross ms6 into the 34 lines is outlined in Table 2. ents. Of these lines, 24 are cosegregating W1 w1 Ms6 Data obtained from testcross and F2-family segregations ms6 and 10 are w1 w1 Ms6 ms6 lines. In addition, these were used to calculate recombination values. Data were sum34 lines are available in both the donor cytoplasm marized across all cytoplasms and subdivided into the ms6w1 donor cytoplasm and also combined across all recurrent (T295H) and the recurrent parent cytoplasms. The availparent cytoplasms. ability of these lines, with the adaptation of the cosegregIn Season 13, the reciprocal cross combinations were evaluation method to produce large quantities of hybrid seed, ated as BC7F2 families. The genotypes of the BC7F1 plants will be useful in research on commercialization of hybrid (testcrosses) were determined by the BC7F2 segregation. Assoybean and on recurrent selection (Lewers and Palsuming no linkage, the expected frequency of BC7F1 genomer, 1997). types when both male sterility and flower color are cosegregatIt is important to know if recombination in the Ms6ing is 1 Ms6 Ms6 W1 W1 : 1 Ms6 Ms6 W1 w1 : 1 Ms6 ms6 W1 chromosome region is affected by intrinsic and (or) W1 W1 : 1 Ms6 ms6 W1 w1. The observed segregation was extrinsic factors. The recombination values will detercompared with the expected 1: 1: 1: 1 segregation by x analysis. mine the resources (seed and land), and environment, x Values were calculated and were highly significant. Recomthat are necessary to maximize hybrid seed production bination values were obtained by using the computer program per unit of land area. The objective was to determine Linkage-1 (Suiter et al., 1983), which uses the maximum likelihood method (Allard, 1956). the recombination values between the Ms6 and W1 loci In season 13, the BC7F2 families were classified into four in the ms6-w1 donor cytoplasm and the recurrent parent genotypic groups. Within BC7F2 families, segregating for both cytoplasms. Linkage determinations were made based male sterility and flower color, 16 fertile plants were singleupon testcrosses and F2-family segregation. plant threshed and evaluated as BC7F2 plant-progeny rows the following summer. The observed segregation data are MATERIALS AND METHODS based upon a total of 800 families (16 plants 3 two cytoplasm classes 3 24 lines). (One line, P596-13 was represented by 32 The 34 recurrent parents used in the male-sterile conversion program are listed in Table 1. Nine of the recurrent parents families 3 two cytoplasm classes.) Six genotypic groups were Table 2. Schedule to generate Ms6 ms6 backcross-derived soybean lines. Season Location Year Procedure 1 Ames, IA 1987 Pollinate donor parent ms6 ms6 w1 w1 plants with recurrent parent to make F1. 2 Ames, IA 1988 Pollinate F1 with recurrent parent to make BC1F1. 3 Isabella, PR 1988/89 Advance BC1FI to BC1F2. 4 Ames, IA 1989 Pollinate BC1F2 ms6 ms6 plants with recurrent parent to make BC2F1. 5 Ames, IA 1990 Pollinate BC2F1 with recurrent parent to make BC3F1. 6 Isabella, PR 1990/91 Advance BC3F1 to BC3F2. 7 Ames, IA 1991 Pollinate BC3F2 ms6 ms6 plants with recurrent parent to make BC4F1. 8 Ames, IA 1992 Pollinate BC4F1 with recurrent parent to make BC5F1. 9 Isabella, PR 1992/93 Advance BC5F1 to BC5F2. 10 Ames, IA 1993 Pollinate BC5F2 with recurrent parent to make BC6F1. 11 Ames, IA 1994 Pollinate BC6F1 with recurrent parent to make BC7F1 with donor parent cytoplasm. Pollinate recurrent parent with BC6F1 to make BC7F1 with recurrent-parent cytoplasm. 12 Isabella, PR 1994/95 Advance BC7F1 to BC7F2. 13 Ames, IA 1995 Identify cosegregating families (Ms6 W1 ms6 w1 ) or segregating families (Ms6 ms6 w1 w1 ) from reciprocal crosses. Single-plant thresh 4 plants per entry from 4 entries for a total of 16 plants per cross combination. All families selected should have phenotype of recurrent parents. 14 Ames, IA 1996 Identify cosegregating families (Ms6 W1 ms6 w1 ) or segregating families (Ms6 ms6 w1 w1 ). Select one family per cross combination for seed increase and release. PALMER ET AL.: RECOMBINATION FOR THE MS6 W1 CHROMOSOME REGION IN SOYBEAN 295 Table 4. Recombination values for the ms6-w1 chromosome reobserved for flower color and fertility/sterility. Assuming no gion of soybean within the ms6-w1 donor cytoplasm, recurrent linkage, the expected frequencies of fertile BC7F2 genotypes parent cytoplasms, and combined across all cytoplasms. Testare shown in Table 3. cross data from the 24 purple-flowered lines used to produce Following Mather (1951), we derived the maximum likelithe cosegregating (Ms6 W1 ms6 w1) lines for the male-sterile hood estimator for recombination frequency (r̂) from this sixconversion program. class segregation as the value of r that satisfied the following Cytoplasm classes and number of testcrosses equation: ms6-w1 donor Recurrent parent Classes All cytoplasms cytoplasm cytoplasms 2nA r 1 (nB 1 nD 1 nE)(1 2 2r)